manuals: add section about the SGs interface.

The SGs interface is currently only casually mentioned in the chapter
running, even though the SGs interface is a prominent and often
requested feature. Let's give the SGs interface its own section so that
users can find the info about it quicker.

Related: OS#6008
Change-Id: Ic7c17511ee19cb7f6d5069b27beb661ecb4b0be8
diff --git a/doc/manuals/chapters/running.adoc b/doc/manuals/chapters/running.adoc
index d6e734b..3041145 100644
--- a/doc/manuals/chapters/running.adoc
+++ b/doc/manuals/chapters/running.adoc
@@ -74,15 +74,8 @@
 
 More on MNCC in <<mncc-external>>.
 
-The SGs interface by default listens on 0.0.0.0:29118. Configure a different IP and/or port for each osmo-msc instance.
-You may also want to configure different VLR names:
-
-----
-sgs
- local-ip 127.0.0.1
- local-port 29118
- vlr-name vlr.example.net
-----
+The SGs interface by default listens on 0.0.0.0:29118 (SCTP). Each instance of OsmoMSC must use a different IP address
+and/or port. For details about the configuration of the SGs interface, see section <<sgs>>.
 
 For the following links, OsmoMSC acts as a client and does not listen/bind to a
 specific interface, and will hence not encounter conflicts for multiple instances