Change docs links to actual file extension (.md)

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

Change-Id: If9d4f0726a0d8d3ca66f01819eeada2b53ac41be
diff --git a/src/main/resources/Documentation/hooks.md b/src/main/resources/Documentation/hooks.md
index 6b0e0ea..2bd19d3 100644
--- a/src/main/resources/Documentation/hooks.md
+++ b/src/main/resources/Documentation/hooks.md
@@ -148,5 +148,5 @@
   cla-signed --submitter <submitter> --user-id <user_id> --cla-id <cla_id>
 ```
 
-[1]: config.html#hooks.syncHookTimeout
+[1]: config.md#hooks.syncHookTimeout
 [2]: ../../../Documentation/json.html#patchSet