[gobject-introspection] Document the newly added GI_HOST_OS envvar

[Emmanuele Bassi <ebassi src gnome org>]

commit 4e20fc1a5e54452ddb9294046daa208125db921a
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Jan 25 22:13:51 2018 +0000

    Document the newly added GI_HOST_OS envvar
    
    https://bugzilla.gnome.org/show_bug.cgi?id=761985

 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 2fbc1d6..f027fdb 100644
--- a/docs/g-ir-scanner.1
+++ b/docs/g-ir-scanner.1
@@ -140,6 +140,10 @@ 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.
+
+The variable GI_HOST_OS can be used to control the OS name on the
+host that runs the scanner. It has the same semantics as the Python
+os.name property.
 .SH BUGS
 Report bugs at http://bugzilla.gnome.org/ in the gobject-introspection product.
 .SH HOMEPAGE and CONTACT