Document which files glib-compile-schemas looks at

Otherwise, your vendor override files are silently ignored...

docs/reference/gio/glib-compile-schemas.xml

@@ -40,6 +40,8 @@ In addition to schema files, glib-compile-schemas reads 'vendor override'
 files, which are key files that can override default values for keys in
 the schemas. The group names in the key files are the schema id, and the
 values are written in serialized GVariant form.
+Vendor ovrride files must have the filename extension
+<filename>.gschema.override</filename>.
 </para>
 
 <refsect2><title>Options</title>

gio/gsettings.c

@@ -96,6 +96,8 @@
  * described by the following DTD:
  * |[<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="text" href="../../../../gio/gschema.dtd"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT</xi:fallback></xi:include>]|
  *
+ * glib-compile-schemas expects schema files to have the extension <filename>.gschema.xml</filename>
+ *
  * At runtime, schemas are identified by their id (as specified
  * in the <tag class="attribute">id</tag> attribute of the
  * <tag class="starttag">schema</tag> element). The
@@ -200,6 +202,10 @@
  *     key2=1.5
  *     </programlisting></informalexample>
  *   </para>
+ *   <para>
+ *     glib-compile-schemas expects schema files to have the extension
+ *     <filename>.gschema.override</filename>
+ *   </para>
  * </refsect2>
  *
  * <refsect2>