📝 README Updates (#24564)

README.md

 Additional documentation can be found at the [Marlin Home Page](https://marlinfw.org/).
 Please test this firmware and let us know if it misbehaves in any way. Volunteers are standing by!
 
-## Marlin 2.0 Bugfix Branch
+## Marlin 2.1 Bugfix Branch
 
 __Not for production use. Use with caution!__
 
-Marlin 2.0 takes this popular RepRap firmware to the next level by adding support for much faster 32-bit and ARM-based boards while improving support for 8-bit AVR boards. Read about Marlin's decision to use a "Hardware Abstraction Layer" below.
+Marlin 2.1 takes this popular RepRap firmware to the next level by adding support for much faster 32-bit and ARM-based boards while improving support for 8-bit AVR boards. Read about Marlin's decision to use a "Hardware Abstraction Layer" below.
 
-This branch is for patches to the latest 2.0.x release version. Periodically this branch will form the basis for the next minor 2.0.x release.
+This branch is for patches to the latest 2.1.x release version. Periodically this branch will form the basis for the next minor 2.1.x release.
 
 Download earlier versions of Marlin on the [Releases page](https://github.com/MarlinFirmware/Marlin/releases).
 
 
 Before building Marlin you'll need to configure it for your specific hardware. Your vendor should have already provided source code with configurations for the installed firmware, but if you ever decide to upgrade you'll need updated configuration files. Marlin users have contributed dozens of tested example configurations to get you started. Visit the [MarlinFirmware/Configurations](https://github.com/MarlinFirmware/Configurations) repository to find the right configuration for your hardware.
 
-## Building Marlin 2.0
+## Building Marlin 2.1
 
-To build Marlin 2.0 you'll need [Arduino IDE 1.8.8 or newer](https://www.arduino.cc/en/main/software) or [PlatformIO](https://docs.platformio.org/en/latest/ide.html#platformio-ide). We've posted detailed instructions on [Building Marlin with Arduino](https://marlinfw.org/docs/basics/install_arduino.html) and [Building Marlin with PlatformIO for ReArm](https://marlinfw.org/docs/basics/install_rearm.html) (which applies well to other 32-bit boards).
+To build Marlin 2.1 you'll need [Arduino IDE 1.8.8 or newer](https://www.arduino.cc/en/main/software) or [PlatformIO](https://docs.platformio.org/en/latest/ide.html#platformio-ide). We've posted detailed instructions on [Building Marlin with Arduino](https://marlinfw.org/docs/basics/install_arduino.html) and [Building Marlin with PlatformIO for ReArm](https://marlinfw.org/docs/basics/install_rearm.html) (which applies well to other 32-bit boards).
 
 ## Hardware Abstraction Layer (HAL)
 
-Marlin 2.0 introduces a layer of abstraction so that all the existing high-level code can be built for 32-bit platforms while still retaining full 8-bit AVR compatibility. Retaining AVR compatibility and a single code-base is important to us, because we want to make sure that features and patches get as much testing and attention as possible, and that all platforms always benefit from the latest improvements.
+Marlin 2.0 introduced a layer of abstraction to allow all the existing high-level code to be built for 32-bit platforms while still retaining full 8-bit AVR compatibility. Retaining AVR compatibility and a single code-base is important to us, because we want to make sure that features and patches get as much testing and attention as possible, and that all platforms always benefit from the latest improvements.
 
 ### Supported Platforms
 
   [STM32F103](https://www.st.com/en/microcontrollers-microprocessors/stm32f103.html)|ARM® Cortex-M3|Malyan M200, GTM32 Pro, MKS Robin, BTT SKR Mini
   [STM32F401](https://www.st.com/en/microcontrollers-microprocessors/stm32f401.html)|ARM® Cortex-M4|ARMED, Rumba32, SKR Pro, Lerdge, FYSETC S6, Artillery Ruby
   [STM32F7x6](https://www.st.com/en/microcontrollers-microprocessors/stm32f7x6.html)|ARM® Cortex-M7|The Borg, RemRam V1
+  [STM32G0B1RET6](https://www.st.com/en/microcontrollers-microprocessors/stm32g0x1.html)|ARM® Cortex-M0+|BigTreeTech SKR mini E3 V3.0
+  [STM32H743xIT6](https://www.st.com/en/microcontrollers-microprocessors/stm32h743-753.html)|ARM® Cortex-M7|BigTreeTech SKR V3.0, SKR EZ V3.0, SKR SE BX V2.0/V3.0
   [SAMD51P20A](https://www.adafruit.com/product/4064)|ARM® Cortex-M4|Adafruit Grand Central M4
   [Teensy 3.5](https://www.pjrc.com/store/teensy35.html)|ARM® Cortex-M4|
   [Teensy 3.6](https://www.pjrc.com/store/teensy36.html)|ARM® Cortex-M4|

ini/stm32f1-maple.ini

 upload_protocol = serial
 
 #
-# BigTree SKR Mini V1.1 / SKR Mini E3 & MZ (STM32F103RCT6 ARM Cortex-M3)
+# BigTreeTech SKR Mini V1.1 / SKR Mini E3 & MZ (STM32F103RCT6 ARM Cortex-M3)
 #
 #   STM32F103RC_btt_maple ............. RCT6 with 256K
 #   STM32F103RC_btt_USB_maple ......... RCT6 with 256K (USB mass storage)
 board_build.ldscript = crealityPro.ld
 
 #
-# BigTree SKR Mini E3 V2.0 & DIP / SKR CR6 (STM32F103RET6 ARM Cortex-M3)
+# BigTreeTech SKR Mini E3 V2.0 & DIP / SKR CR6 (STM32F103RET6 ARM Cortex-M3)
 #
 #   STM32F103RE_btt_maple ............. RET6
 #   STM32F103RE_btt_USB_maple ......... RET6 (USB mass storage)

ini/stm32f1.ini

 monitor_speed = 115200
 
 #
-# BigTree SKR Mini V1.1 / SKR Mini E3 & MZ (STM32F103RCT6 ARM Cortex-M3)
+# BigTreeTech SKR Mini V1.1 / SKR Mini E3 & MZ (STM32F103RCT6 ARM Cortex-M3)
 #
 #   STM32F103RC_btt ............. RCT6 with 256K
 #   STM32F103RC_btt_USB ......... RCT6 with 256K (USB mass storage)
 board   = genericSTM32F103RC
 
 #
-# BigTree SKR Mini E3 V2.0 & DIP / SKR CR6 (STM32F103RET6 ARM Cortex-M3)
+# BigTreeTech SKR Mini E3 V2.0 & DIP / SKR CR6 (STM32F103RET6 ARM Cortex-M3)
 #
 #   STM32F103RE_btt ............. RET6
 #   STM32F103RE_btt_USB ......... RET6 (USB mass storage)

ini/stm32g0.ini

 #################################
 
 #
-# BigTree SKR mini E3 V3.0 (STM32G0B1RET6 ARM Cortex-M0+)
+# BigTreeTech SKR mini E3 V3.0 (STM32G0B1RET6 ARM Cortex-M0+)
 #
 [env:STM32G0B1RE_btt]
 extends                     = stm32_variant