docs: Add a Richer README.md file

Add features, communication & contribution, build information,
and usage of Geoclue.

Fixes #108
4 jobs for dev in 15 minutes and 53 seconds (queued for 154 minutes and 16 seconds)
Status Job ID Name Coverage
  Test
passed #174815
ubuntu-16.04

00:04:23

passed #174816
ubuntu-17.10

00:04:57

passed #174817
ubuntu-18.04

00:02:57

passed #174818
ubuntu-18.04-no-backend

00:03:35