docs: Fix links and compiling instructions
docs: Fix links and compiling instructions

 * Links are now pointing to GNOME gitlab
 * Compiling instructions are now using meson/ninja
 * Removing unmaintained Ubuntu's PPA

Signed-off-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@gnome.org>

jasuarez/grilo,jasuarez/grilo,GNOME/grilo,GNOME/grilo,grilofw/grilo,grilofw/grilo,jasuarez/grilo,grilofw/grilo