Documentation: add warning to "creating an addon" (#319)

* Documentation: add warning to "creating an addon"

* Use info instead of error

Co-authored-by: Hans5958 <hans5958@outlook.com>

---------

Co-authored-by: Hans5958 <hans5958@outlook.com>

content/docs/develop/getting-started/creating-an-addon.md

@@ -7,6 +7,15 @@ aliases:
 Required software: text editor, Chrome.  
 If possible, disable the Scratch Addons extension you downloaded from the store before proceeding to avoid issues.
 
+
+{{< admonition info >}}
+If you plan to submit the addon you are developing as a pull request to our GitHub repository, please read our [contributing guidelines](https://github.com/ScratchAddons/ScratchAddons/blob/master/.github/CONTRIBUTING.md) first. 
+
+In case there is no existing GitHub issue in that repository related to your new addon idea, please [create one](https://github.com/ScratchAddons/ScratchAddons/issues/new/choose). However, if there is already an issue related to your feature idea, we suggest that you leave a comment on it stating your intention to develop the addon. This will enable other contributors to provide feedback on whether the addon could be accepted, or if further discussion is required.
+
+However, if you are creating an addon for personal use, you may proceed with this guide.
+{{< /admonition >}}
+
 ## Step 1: Read about [addon basics](/docs/develop/getting-started/addon-basics/)
 Make sure to read that article to be familiar with the terminology.