docs: Update document on how to build using meson
The documentation on how to build Grilo was out-of-date after the port from autotools to meson. This commit also contains the update needed after the migration to the gitlab.gnome.org
The documentation on how to build Grilo was out-of-date after the port from autotools to meson. This commit also contains the update needed after the migration to the gitlab.gnome.org