Improve socialtodos docs

While the last two sections are still missing, I think this is great as
a first version. We can improve it incrementally and it is already much
better than what we have.

Done-with: Harri Eronen

Change-Id: Ife54cbf75814742d88a43db298c4ccac2f29f55a
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Update docs after search function has been renamed.

Change-Id: I83a9b6a8b029723d6ec718fa47451cdda3b16bdd
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>