[gnome-contacts] README.md: update after migrating to GitLab.

[Niels De Graef <nielsdg src gnome org>]

commit ffdf24538e781c60d1542a9bbb6e20f434ebedeb
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Wed Jan 24 17:32:44 2018 +0100

    README.md: update after migrating to GitLab.

 README.md | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)
---
diff --git a/README.md b/README.md
index d868da7..c71d9ff 100644
--- a/README.md
+++ b/README.md
@@ -11,23 +11,18 @@ ninja -C build install
 ```
 
 ## Issue tracker
-Contacts uses the GNOME Bugzilla, where you can check the
-[list of open bugs](https://bugzilla.gnome.org/browse.cgi?product=gnome-contacts).
-
-If you'd like to report a bug in Contacts or request an enhancement, please file
-an issue using the
-[appropriate form](https://bugzilla.gnome.org/enter_bug.cgi?product=gnome-contacts).
-
-In case of a bug, please also add reproducible steps and the version of Contacts.
-
-## Contributing
-If you would like to contribute a patch, you should send it in to the GNOME
-Bugzilla as well. If the patch fixes an existing bug, add the patch as an
-attachment to that bug report; otherwise, enter a new bug report that describes
-the patch, and attach the patch to that bug report.
-
-For more information on the recommended workflow, please read
-[this wiki page](https://wiki.gnome.org/Git/WorkingWithPatches).
+The code and issue tracker of Contacts can be found at the
+[gnome-contacts repository](https://gitlab.gnome.org/GNOME/gnome-contacts) on
+the GNOME GitLab instance.
+
+If you find a bug in Contacts, please file an issue with reproducible steps and
+the version of Contacts (shown in the About dialog, or by running
+`gnome-contacts --version`).
+
+If you want to contribute functionality or bug fixes to Contacts, you should
+fork the Contacts repository, work on a separate branch, and then open a
+merge request (MR) on our GitLab repository. If the MR fixes an existing issue,
+please refer to that issue in the description.
 
 ## More information
 Contacts has its own web page on https://wiki.gnome.org/Apps/Contacts.