README.md: Change mailing list address to osmocom.org

Change-Id: Ie7b474138444f0ceea160f74df4b693030ea07a8
diff --git a/README.md b/README.md
index 6992361..cf70f44 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@
 ============
 Current gr-gsm project's mailing list address is following:
 
-gr-gsm@googlegroups.com
+gr-gsm@lists.osmocom.org
 
 Mailing list is a place for general discussions, questions about the usage and installation. In case of problem with installation please try to provide full information that will help reproducing it. Minimum information should contain:
 - operating system with version,
@@ -20,9 +20,9 @@
 - version of gnuradio (it can be obtained with: gnuradio-companion --version)
 - error messages (in case of pybombs installation they can be obtained after switching it to verbous mode with -v option).
 
-To join the group with any e-mail addres (google account is not required) use this link:
+To join the group with any e-mail address, use this link:
 
-https://groups.google.com/forum/#!forum/gr-gsm/join
+https://lists.osmocom.org/mailman/listinfo/gr-gsm
 
 Development
 ===========