tweak

README_Building.md

@@ -16,12 +16,10 @@ make clean && make
 * ```RELEASE=1``` for performance and code size, without it, assertions are kept for debugging.
 * ```DEBUG=1``` is available.
 
-## Under Linux
+## Under Linux (recommended)
 
 Espruino is easy to build under Linux, for either for Espruino running on Linux or a board.
 
-The current reference OS for building is Ubuntu 16.04.1 LTS, and the following can ensure problem free development:
-
 ### Easy Method : provision.sh
 
 Simply run the following with the name of your board to set
@@ -35,7 +33,10 @@ This should work for common platforms on Linux, but will only set
 paths up for your current session. You'll have to run it again
 next time you log in.
 
-### for Espruino
+### Manual Method
+
+#### For Espruino
+
 
 ```bash
 sudo apt-get update
@@ -51,7 +52,7 @@ make clean && make
 chmod +x espruino && sudo cp espruino /usr/local/bin
 ```
 
-### for an example of cross compilation for Puck.js
+#### for cross compilation to Puck.js
 
 Having successfully created an native OS Espruino, try a cross compilation.