This guide assumes, that you have
svn already installed on your QNAP, fully configured and working like a charm, and you just want to enhance it with web client (WebSVN). You can use this guide also on any other server, than QNAP, but keep in mind, that it contains some QNAP-specific problems.
Keep in mind: WebSVN (as good as all other alternatives mentioned in the end of this text) are read-only web SVN clients! You can do a lot of useful stuff on your repos, but forget about committing or anything similar that requires write access or changing repository structure.