Remove obsolete reference to site.enableSrcToMarkdown

That config option has never been in mainline Gerrit, and it isn't
needed for plugin's operation anyway.

Change-Id: Ic7b9dfd386be95ad67494e436df330d6808e5039

src/main/resources/Documentation/about.md

diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index ab89d44..c8fc4bd 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -21,11 +21,9 @@
   and [Push](../../../Documentation/access-control.html#category_push)
   to enable users to upload images.
 
-In addition Gerrit must be
-[configured to serve project documentation from Markdown](../../../Documentation/config-gerrit.html#site.enableSrcToMarkdown)
-to make images available for browsing. Also the image mime types must be
-[configured as safe](../../../Documentation/config-gerrit.html#mimetype.name.safe)
-because otherwise Gerrit refuses to render the images.
+In addition Gerrit must be configured to
+[treat the image MIME types as safe](../../../Documentation/config-gerrit.html#mimetype.name.safe)
+because otherwise they would not get rendered.
 
 To allow deletions of own uploaded images the global capability
 `Delete Own Images` can be granted.