Add documentation for running local generators (#547)

Author: elevenpassin

lib/usage.txt

@@ -15,6 +15,12 @@ Install a generator:
   $ npm install generator-angular
   $ yo angular --help
 
+Run local generators:
+  
+  Additionally, you can also run local generators without installing via npm.
+
+  $ yo ./path/to/some/generator
+
 Completion:
 
   To enable shell completion for the yo command, try running

readme.md

@@ -27,6 +27,12 @@ yo webapp
 
 *To create and distribute your own generator, refer to [our official documentation](http://yeoman.io/authoring/)*
 
+You can also run a local generator on your computer as such:
+
+```sh
+# Running a local generator
+yo ./path/to/local/generator
+```
 
 ## Options