[gtk/man-page-improvement] docs: Improve the gtk4-launch man page

[Matthias Clasen <matthiasc src gnome org>]

commit c609e2fef9645f9e5a280915952c42b9685d7523
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Jul 3 15:22:43 2021 -0400

    docs: Improve the gtk4-launch man page
    
    Be more precise about where desktop files are found.
    
    Fixes: #4081

 docs/reference/gtk/gtk4-launch.xml | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)
---
diff --git a/docs/reference/gtk/gtk4-launch.xml b/docs/reference/gtk/gtk4-launch.xml
index aeb5e8dca1..8ee32141a0 100644
--- a/docs/reference/gtk/gtk4-launch.xml
+++ b/docs/reference/gtk/gtk4-launch.xml
@@ -46,7 +46,8 @@ display, unless specified otherwise.
 <para>
 <command>gtk4-launch</command> takes at least one argument, the name of
 the application to launch. The name should match application desktop file name,
-as residing in /usr/share/application, with or without the '.desktop' suffix.
+as residing in the applications subdirectories of the XDG data directories, with
+or without the '.desktop' suffix.
 </para>
 <para>
 If called with more than one argument, the rest of them besides the application
@@ -71,4 +72,14 @@ application.
   </variablelist>
 </refsect1>
 
+<refsect1><title>Environment</title>
+  <para>Some environment variables affect the behavior of <command>gtk4-launch</command>.</para>
+  <variablelist>
+    <varlistentry>
+    <term><option>XDG_DATA_HOME</option>, <option>XDG_DATA_DIRS</option></term>
+      <listitem><para>The environment variables specifying the XDG dta directories.</para></listitem>
+    </varlistentry>
+  </variablelist>
+</refsect1>
+
 </refentry>