Change docs links to actual file extension (.md)

See https://gerrit-review.googlesource.com/83950 for detailed context.

Change-Id: I8fd98395cf7aebb1dfe06c223a3c75b85b6fcddd

src/main/resources/Documentation/about.md

diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index f887cca..e12f31a 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -10,4 +10,4 @@
 
 For this to work, http must be enabled in both instances and the plugin
 must be configured with valid credentials. For further information, refer to
-[config](config.html) documentation.
+[config](config.md) documentation.