Add mention of working on a Plone project as a requirement, and how using filters for finding appropriate issues to work on

Author: stevepiercy

docs/contributing/first-time.md

@@ -17,6 +17,7 @@ As a first-time contributor to Plone, we expect that you have:
 
 -   {ref}`tried a Plone demo <install-index-getting-started-label>`
 -   {doc}`installed Plone <../install/index>` on your development machine
+-   worked on a Plone project, even if it is just for fun
 -   worked through some trainings, such as the recommended:
     -   {doc}`training:mastering-plone/index`
     -   {doc}`training:voltohandson/index`
@@ -106,8 +107,11 @@ Please don't be "that person".
 ### Work with GitHub issues
 
 1.  **Find issues that you want to work on.**
+    You can filter GitHub issues by labels.
     Working on documentation or on issues labeled with either `33 needs: docs` or `41 lvl: easy` are the two best ways for first-time contributors to contribute.
     This is because first-timers have a fresh perspective that might be overlooked by old-timers.
+    Issues labeled `42 lvl: moderate`, `43 lvl: complex`, or `03 type: feature (plip)` are not suitable for first-timers because of their complexity.
+    Issues with these labels may take weeks to complete.
 1.  **Discuss whether you should perform any work.**
     First see {ref}`Avoid duplicate effort <mistake-2-label>`.
     Next, any discussion method listed below is acceptable, and they are listed in the order of most likely to get a response.