Minor corrections to coderef topic
Update `dita` command description

* Add `install-dir` & `output-dir` to parameter list
* Sync "no news is good news" info from quickstart variant
* Sync argument order in sample codeblock
Point distribution download links to dita-ot.org

Remove remaining SourceForge references & avoid explicit link to GitHub release tag to simplify maintenance.

(The dita-ot.org/download page uses the `{{site.release}}` variable to point to the latest distribution packages on GitHub.)