build cleanups

* update docs to simplify build steps
* Gemfile.lock seemed to have an older version specified
* do not check in the pkg dir

ruby/README.md

diff --git a/ruby/README.md b/ruby/README.md
index d2fa76a..9ae3ac3 100644
--- a/ruby/README.md
+++ b/ruby/README.md
@@ -76,7 +76,7 @@
 Then build the Gem:
 
     $ rake gem
-    $ gem install pkg/protobuf-$VERSION.gem
+    $ gem install `ls pkg/google-protobuf-*.gem`
 
 To run the specs: