[gtksourceview] readme: add instructions to build GSV from Git

[Sébastien Wilmet <swilmet src gnome org>]

commit c6c4e32f39ef44864233f4368f3db49ffb9dcb9b
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Fri Jun 17 19:51:24 2016 +0200

    readme: add instructions to build GSV from Git

 README |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/README b/README
index cc2c171..ff9b929 100644
--- a/README
+++ b/README
@@ -40,6 +40,14 @@ Simple install procedure:
 
 See the file 'INSTALL' for more detailed information.
 
+From the Git repository, the 'configure' script and the 'INSTALL' file are not
+yet generated, so you need to run 'autogen.sh' instead, which takes the same
+arguments as 'configure'.
+
+To build the latest version of GtkSourceView from Git, Jhbuild can be used:
+
+    https://wiki.gnome.org/Projects/Jhbuild
+
 
 How to report bugs
 ==================