Merge pull request rubygems#1796 from Fluxx/add_docs_for_no_cache

Add docs for the --no-cache option

man/bundle-install.ronn

@@ -10,6 +10,7 @@ bundle-install(1) -- Install the dependencies specified in your Gemfile
                  [--binstubs[=DIRECTORY]]
                  [--standalone[=GROUP1[ GROUP2...]]]
                  [--quiet]
+                 [--no-cache]
 
 ## DESCRIPTION
 
@@ -81,6 +82,11 @@ update process below under [CONSERVATIVE UPDATING][].
   `bundle` directory and installs the bundle there. It also generates
   a `bundle/bundler/setup.rb` file to replace Bundler's own setup.
 
+* `--no-cache`:
+  Do not update the cache in `vendor/cache` with the newly bundled gems. This
+  does not remove any existing cached gems, only stops the newly bundled gems
+  from being cached during the install.
+
 ## DEPLOYMENT MODE
 
 Bundler's defaults are optimized for development. To switch to