Log when a key is _not_ used as a deploy key

Resolves #69.

Co-authored-by: Sean Killeen <SeanKilleen@gmail.com>

index.js

@@ -53,6 +53,8 @@ try {
         const parts = key.match(/\bgithub\.com[:/]([_.a-z0-9-]+\/[_.a-z0-9-]+)/i);
 
         if (!parts) {
+            console.log(`Comment for key '${key}' does not match GitHub URL pattern. Not treating it as a GitHub deploy key.`);
+
             return;
         }