[gobject-introspection] g-ir-scanner: document GI_SCANNER_DEBUG in man page

[Sebastian Geiger <segeiger src gnome org>]

commit 579a018cf5fa64e73946db0788ea236d402c3a00
Author: Sebastian Geiger <sbastig gmx net>
Date:   Sat Feb 11 22:09:52 2017 +0100

    g-ir-scanner: document GI_SCANNER_DEBUG in man page
    
    https://bugzilla.gnome.org/show_bug.cgi?id=778509

 docs/g-ir-scanner.1 |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/docs/g-ir-scanner.1 b/docs/g-ir-scanner.1
index 522e9eb..2fbc1d6 100644
--- a/docs/g-ir-scanner.1
+++ b/docs/g-ir-scanner.1
@@ -136,6 +136,10 @@ set on a distribution so you shouldn't need to set it yourself.
 
 The variable GI_SCANNER_DISABLE_CACHE ensures that the scanner will
 not write cache data to $HOME.
+
+The variable GI_SCANNER_DEBUG can be used to debug issues in the build-system that
+involve g-ir-scanner. When it is set to 'save-temps', then g-ir-scanner will not remove
+temporary files and directories after it terminates.
 .SH BUGS
 Report bugs at http://bugzilla.gnome.org/ in the gobject-introspection product.
 .SH HOMEPAGE and CONTACT