Add checkdeps

Developer-Guide.md

@@ -49,6 +49,10 @@ The minimum requirements are:
 
 The executables `git`, `java`, `jar`, and `python` should be in your `PATH`.
 
+You can check your configuration by running:
+
+    $ ./build.py checkdeps
+
 To install the Node.js dependencies run
 
     $ npm install