Update README.md

Should this be "Deleting own posts"? Deleting own topics is already mentioned under "Topics".
oversight and useless routes removed for topic#index and posts#index actions
Merge pull request #615 from yahor/rails4

oversight and useless routes removed for topic#index and posts#index act...
Bump to 4.1.7
Support any Rails 4.0 and less than 4.2
polish translation equal to english
Merge pull request #620 from h3xed/polish_translation

polish translation equal to english
Merge pull request #562 from chrisalley/patch-1

Update README.md
Merge remote-tracking branch 'radar/rails4' into rails4