document doc:* rake tasks

railties/guides/source/command_line.textile

@@ -398,7 +398,13 @@ More information about migrations can be found in the "Migrations":migrations.ht
 
 h4. +doc+
 
-If you want to strip out or rebuild any of the Rails documentation (including this guide!), the +doc:+ namespace has the tools. Stripping documentation is mainly useful for slimming your codebase, like if you're writing a Rails application for an embedded platform.
+The +doc:+ namespace has the tools to generate documentation for your app, API documentation, guides. Documentation can also be stripped which is mainly useful for slimming your codebase, like if you're writing a Rails application for an embedded platform.
+
+* +rake doc:app+ generates documentation for your application in +doc/app+.
+* +rake doc:guides+ generates Rails guides in +doc/guides+.
+* +rake doc:rails+ generates API documentation for Rails in +doc/api+.
+* +rake doc:plugins+ generates API documentation for all the plugins installed in the application in +doc/plugins+.
+* +rake doc:clobber_plugins+ removes the generated documentation for all plugins.
 
 h4. +notes+