[libchamplain] Add a comment to .gitignore about the _ prefix for meson build dir

[Jiří Techet <jiritechet src gnome org>]

commit b6f17ce1ba6b862b6b55bd9c66a01d0d88e151a3
Author: Jiří Techet <techet gmail com>
Date:   Mon Feb 18 16:28:15 2019 +0100

    Add a comment to .gitignore about the _ prefix for meson build dir

 .gitignore | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/.gitignore b/.gitignore
index 91408e4..179de25 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,6 @@
+# prefix the meson build directory with _ to get it ignored
+_*
+
 Makefile
 Makefile.in
 aclocal.m4
@@ -17,7 +20,6 @@ autom4te.cache
 *#*
 *.sw?
 *.pyc
-_*
 champlain-gtk/champlain-gtk-marshal.c
 champlain-gtk/champlain-gtk-marshal.h
 champlain-gtk/stamp-marshal