docs: update source-code-management.txt

Reported-by: J William Piggott <elseifthen@gmx.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

Documentation/source-code-management.txt

@@ -1,6 +1,16 @@
 SCM (source code management):
 
-    git clone git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git util-linux
+    Primary repository:
+	git clone git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git util-linux
+
+    Backup repository:
+	git clone git://github.com/karelzak/util-linux.git
+
+Note that GitHub repository may contain temporary development branches too.
+
+The kernel.org repository contains master (current development) and stable/*
+(maintenance) branches only. All master or stable/* changes are always pushed
+to the both repositories in the same time.
 
 Branches:
 
@@ -8,12 +18,6 @@ Branches:
 	- created for every <major>.<minor> release
 	- branch name: stable/v<major>.<minor>
 
-    * bugfix branch
-	- created for <major>.<minor>.<maint> release for
-	  critical/security bugs only
-	- this branch is optional
-	- branch name: stable/v<major>.<minor>.<maint>
-
     * master branch
 	- the status of this branch is: "it works for me". It
 	  means useful but not well tested patches.
@@ -22,8 +26,13 @@ Branches:
 	  an active development forked into a separate branch
 	  (topic branches) from the tip of "master".
 
+Tags:
+
     * A new tag object is created for:
-	- every release, tag name: v<version>
+	- every release, tag name: v<version>, see "git tag -l" for
+          more information
+        - all tags are signed by maintainer's PGP key
 
     * KNOWN BUGS:
-	- tag v2.13.1 is typo. Please, ignore this tag.
+	- don't use tag v2.13.1 (created and published by mistake),
+          use v2.13.1-REAL.