Added a short description on how to add mruby gems to the compilation workflow.

INSTALL

@@ -28,6 +28,20 @@ send a detailed report to the developers that includes the error log, machine,
 and OS type.
 
 
+* Adding existing gems
+
+Gems from the [list of mruby gems](http://www.mruby.org/libraries/) can be added by adding
+their respective GitHub URLs to build_config.rb. For example, to add implementations of the
+File and IO Ruby core classes to mruby, insert the following in build_config.rb under the
+comment section `Use mrbgems`:
+
+    conf.gem :git => 'git@github.com:iij/mruby-io.git', :branch => 'master'
+
+    Afterwards, re-run:
+
+        ruby ./minirake
+
+
 * Porting to other platforms
 
 

README.md

@@ -41,7 +41,7 @@ The URL of the mruby home-page is:
 To subscribe to the mruby mailing list....[T.B.D.]
 
 
-## How to compile and install
+## How to compile and install (mruby and gems)
 
 See the INSTALL file.