Fix Markdown rendering issue

The example plugin config fragment wasn't rendered as a code block.

Change-Id: Iff9f003b5b6b8edf2fc02f937669a03daf6a8b4e
diff --git a/src/main/resources/Documentation/log-level.md b/src/main/resources/Documentation/log-level.md
index bb90dd5..639a2d4 100644
--- a/src/main/resources/Documentation/log-level.md
+++ b/src/main/resources/Documentation/log-level.md
@@ -8,6 +8,7 @@
 SYNOPSIS
 --------
 @PLUGIN@.config:
+
 ```
 [FATAL]
     name = com.google.gerrit.server.change.EmailReviewComments