Document how to limit the RTC integration to certain branches

Change-Id: I857990a84cbc28213952fedf8ef8ec714e02c9a7
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

src/main/resources/Documentation/config.md

diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 701dde6..88acfd4 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -42,6 +42,21 @@
 a project can enforce the RTC integration for all child projects by
 setting `plugin.its-rtc.enabled` to `enforced`.
 
+The RTC integration can be limited to specific branches by setting
+`plugin.its-rtc.branch`. The branches may be configured using explicit
+branch names, ref patterns, or regular expressions. Multiple branches
+may be specified.
+
+E.g. to limit the RTC integration to the `master` branch and all
+stable branches the following could be configured:
+
+```
+  [plugin "its-rtc"]
+    enabled = true
+    branch = refs/heads/master
+    branch = ^refs/heads/stable-.*
+```
+
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