Clarify in documentation that the revision must be URL encoded

Change-Id: Ib05a8b28a674623f3648e6e5c52b95474d21030f
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

src/main/resources/Documentation/about.md

diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index 8e4d020..ef74e0b 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -7,7 +7,8 @@
 
 The file is served from the branch/commit to which `HEAD` points unless
 a revision is specified in the URL as
-`/@PLUGIN@/project/<project-name>/rev/<rev>/<file-name>`.
+`/@PLUGIN@/project/<project-name>/rev/<rev>/<file-name>`. The revision
+must be URL encoded.
 
 ```
   /@PLUGIN@/project/external%2Fopenssl/rev/stable-1.3/docs/faq.md