Update README with version update instruction

Author: headius

README.md

@@ -333,6 +333,7 @@ package and push the .jar every time a commit changes a source file).
 ## Releasing
 
 * Make sure auth is configured for "ossrh" repository ID in your .m2/settings.xml
+* Update the version in src/main/ruby/jruby/rack/version.rb to the release version
 * mvn release:prepare
 * mvn release:perform (possibly with -DuseReleaseProfile=false due to Javadoc doclint failures for now)
 * rake clean gem SKIP_SPECS=true and push the gem
@@ -348,4 +349,4 @@ More information at the [wiki][5] or ask us at **#jruby**'s IRC channel.
 [4]: https://github.com/jruby/jruby-rack/issues
 [5]: https://wiki.github.com/jruby/jruby-rack
 [8]: http://badge.fury.io/rb/jruby-rack
-[9]: https://secure.travis-ci.org/jruby/jruby-rack.png?branch=master
+[9]: https://secure.travis-ci.org/jruby/jruby-rack.png?branch=master