docs: add 'edit this page' link to footer of every page

To encourage contributors to make changes to the main website, add a
footer link to every page which links to the corresponding source file
in git. With gitlab, they are able to edit content directly in the web
browser and then submit a merge request. This gives a way to contribute
content that is arguably easier than our wiki which requires manual
account creation, while this will also benefit from maintainer review.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

docs/site.xsl

@@ -27,6 +27,7 @@
   <xsl:template match="/">
     <xsl:apply-templates select="." mode="page">
       <xsl:with-param name="pagename" select="$pagename"/>
+      <xsl:with-param name="pagesrc" select="$pagesrc"/>
       <xsl:with-param name="timestamp" select="$timestamp"/>
     </xsl:apply-templates>
   </xsl:template>