[gtk/ebassi/for-master] docs: Add missing a11y environment variables

[Emmanuele Bassi <ebassi src gnome org>]

commit 80f6d4f4babf011f831c2a49e2e9188d1fea9abe
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sat Nov 7 12:50:11 2020 +0000

    docs: Add missing a11y environment variables
    
    Mention the GTK_TEST_ACCESSIBLE and GTK_NO_A11Y in the "Running GTK
    applications" section of the GTK API reference.

 docs/reference/gtk/running.md | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/docs/reference/gtk/running.md b/docs/reference/gtk/running.md
index 2135eaa8d5..644ae3a918 100644
--- a/docs/reference/gtk/running.md
+++ b/docs/reference/gtk/running.md
@@ -285,6 +285,17 @@ CSD is always used for windows with a custom titlebar widget set,
 as the WM should not draw another titlebar or other decorations
 around the custom one.
 
+### GTK_TEST_ACCESSIBLE
+
+If set to a non-empty value, it selects the test backend for the GTK
+accessibility API. This backend is useful for performing functional
+testing on your accessible widget state as part of your test suite
+or continuous integration pipeline.
+
+### GTK_NO_A11Y
+
+If set to a non-empty value, it disables the accessibility API entirely.
+
 ### XDG_DTA_HOME, XDG_DATA_DIRS
 
 GTK uses these environment variables to locate icon themes