Docs getting started

Change this named link:
```.. _cross-site request forgery: http://en.wikipedia.org/wiki/Cross-site_request_forgery```
into an anonymous link:
```_ http://en.wikipedia.org/wiki/Cross-site_request_forgery```
and move it right after the text block where the link is used, so Sphinx knows where to replace it.

See: https://community.elgg.org/discussion/view/1833136/what-specific-semantics-are-to-be-known-for-creating-elgg-docs-translations-from-po-files