Add note about Maven repository usage to pom.xml

pom.xml

@@ -74,6 +74,12 @@
     </dependencies>
 
     <repositories>
+        <!--
+            If you are a plugin developer, please use https://hub.spigotmc.org/nexus/content/repositories/snapshots/
+            as your repository URL. This will ensure only Bukkit / Spigot-API are pulled from our Maven repository.
+
+            Please see https://www.spigotmc.org/go/maven for more information.
+        -->
         <repository>
             <id>spigotmc-public</id>
             <url>https://hub.spigotmc.org/nexus/content/groups/public/</url>