[latexila] Add README.md for the GitHub mirror

[Sébastien Wilmet <swilmet src gnome org>]

commit f42437a5fab47cb1717fb0566111e25e4bc91afe
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu Jan 22 18:47:15 2015 +0100

    Add README.md for the GitHub mirror
    
    There are currently two pull requests on GitHub that shouldn't be there,
    so add a warning.

 README.md |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..051f5d0
--- /dev/null
+++ b/README.md
@@ -0,0 +1,9 @@
+README for the GitHub mirror of LaTeXila
+========================================
+
+The LaTeXila repository at GitHub is a **read-only mirror**! Do *not* create
+pull requests there. The purpose is just to ease the creation of clones, so you
+can host your branches.
+
+See the [homepage of LaTeXila](https://wiki.gnome.org/Apps/LaTeXila) to know
+how to contribute.