[libsigcplusplus] website: Mention the GitHub mirror.

[Murray Cumming <murrayc src gnome org>]

commit b89723660340a04feec6154a881ea7a32ab74918
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Mar 18 09:11:00 2016 +0100

    website: Mention the GitHub mirror.

 docs/website/devel.shtml |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/docs/website/devel.shtml b/docs/website/devel.shtml
index 21bae87..a42c98b 100644
--- a/docs/website/devel.shtml
+++ b/docs/website/devel.shtml
@@ -27,11 +27,14 @@ Open <a href="http://bugzilla.gnome.org/buglist.cgi?product=libsigc%2B%2B&bug_st
 Submit a new libsigc++ bug <a href="http://bugzilla.gnome.org/enter_bug.cgi?product=libsigc%2B%2B";>here</a>
 </p>
 
+<p>We also accept pull requests via the <a href="https://github.com/GNOME/libsigcplusplus";>libsigc++ mirror 
on GitHub</a>.</p>
+
 <a name="git"><h3>Version Control</h3></a>
 
 <p>
 libsigc++ is in the <a href="http://git.gnome.org/browse/libsigcplusplus/";>libsigcplusplus</a> module in 
GNOME's git repository.
 </p>
+<p>There is also a <a href="https://github.com/GNOME/libsigcplusplus";>libsigc++ mirror on GitHub</a>.</p>
 
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