Update a05-board-generator.rst (#5093)

Added additional information about where to find the core root directory (often deeply hidden) so users can run board generator

Author: dalbert2

Diff for: doc/faq/a05-board-generator.rst

@@ -34,7 +34,9 @@ It needs to be run from the root directory,
     C:\...> python tools\boards.txt.py
 
 Running without parameters will show the command line help.  They are
-generally self-explanatory.
+generally self-explanatory.  Running with the parameters will show no output but will generate a new boards.txt file (and a backup boards.txt.orig).
+
+The core root directory varies depending on your development environment.  In Windows, core root is found under your home directory; for Arduino it is in AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\ for PlatformIO it is in .platformio\packages\framework-arduinoespressif8266.
 
 
 What can I do with it ?