Add documentation that positive numbers require sign

Change-Id: I05e2f0bfdb5c7df6656662c4726a3b99c7b46055

src/main/resources/Documentation/config.md

diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 758c867..d949c9d 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -124,9 +124,11 @@
 
 `<verified-value>`
 :	Verified flag added on Gerrit with values from -1 to +1
+	For positive values, you must not omit a leading +.
 
 `<code-review-value>`
 :	Code-Review flag added on Gerrit with values from -2 to +2
+	For positive values, you must not omit a leading +.
 
 Note: multiple conditions in the action stanza are optional but at least one must be present.