[jhbuild] docs: add comment about setting buildroot to None

[Sébastien Wilmet <swilmet src gnome org>]

commit 35c6a4d450904b7a1dd5b5cf0fe13e94b8d99b41
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu Sep 1 06:30:23 2016 +0200

    docs: add comment about setting buildroot to None
    
    It's better to set buildroot to None instead of setting the same value
    as checkoutroot.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=770691

 jhbuild/defaults.jhbuildrc |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/jhbuild/defaults.jhbuildrc b/jhbuild/defaults.jhbuildrc
index e6767fa..0ca4ddc 100644
--- a/jhbuild/defaults.jhbuildrc
+++ b/jhbuild/defaults.jhbuildrc
@@ -54,6 +54,7 @@ xdg_cache_home = os.environ.get('XDG_CACHE_HOME',
                                              '.cache'))
 tarballdir = os.path.join(xdg_cache_home, 'jhbuild', 'downloads')
 
+# Set to None to perform builds within the source trees.
 buildroot = os.path.join(xdg_cache_home, 'jhbuild', 'build')
 
 # When using srcdir!=builddir builds, this key allows you to use a