Added readme file for bqh2 and disabled the SLOWDOWN config flag

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

 #define DEFAULT_MINSEGMENTTIME        20000
 
 // If defined the movements slow down when the look ahead buffer is only half full
-#define SLOWDOWN
+//#define SLOWDOWN
 
 // Frequency limit
 // See nophead's blog for more info

Marlin/example_configurations/Hephestos_2/readme.md

+# Example Configuration for BQ [Hephestos 2](http://www.bq.com/uk/hephestos-2)
+This configuration file is based on the original configuration file shipped with the heavily modifiied Marlin fork by BQ. The orignal firmware and configuration file can be found at [BQ Github repository](https://github.com/bq/Marlin).
+
+NOTE: The look and feel of the Hephestos 2 while navigating the LCD menu will change by using the original Marlin firmware.
+
+## Changelog
+* 2016/03/01 - Initial release