Change docs links to actual file extension (.md)

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

Change-Id: Ia88f168c95050659a76956c7b089e005b350ce6b

src/main/resources/Documentation/about.md

diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index 6236e8f..a5adccc 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -7,4 +7,4 @@
 
 For this synchronization 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.
+to [config](config.md) documentation.