feat(folia): document Folia support requirement in plugin.yml (#742)

* Document Folia support requirement in plugin.yml

Added instructions for enabling Folia support in plugins.

* Update isFoliaSupported to folia-supported in docs

* Update src/content/docs/paper/dev/api/folia-support.md

Co-authored-by: Matouš Kučera <mk@kcra.me>

* Update src/content/docs/paper/dev/api/folia-support.md

Co-authored-by: Matouš Kučera <mk@kcra.me>

* chore: stress the importance of developing with Folia in mind

---------

Co-authored-by: Matouš Kučera <mk@kcra.me>

Author: Chamogelastos

src/content/docs/paper/dev/api/folia-support.md

@@ -9,6 +9,20 @@ slug: paper/dev/folia-support
 [Folia](https://github.com/PaperMC/Folia) is a fork of Paper, which is currently maintained by the PaperMC team.
 It adds the ability to split the world into regions as outlined [here](/folia/reference/overview) in more depth.
 
+# Mark plugin as supported on Folia
+
+Plugins can't run on Folia if you don't have this field in your paper-plugin.yml (or plugin.yml, respectively):
+```yaml
+folia-supported: true
+```
+
+:::danger
+
+Marking a plugin as supported on Folia is *not nearly enough* to support Folia.
+You must specially develop your plugin with the intent of supporting Folia, keeping things mentioned on this page in mind.
+
+:::
+
 # Checking for Folia
 
 Depending on what platform your plugin is running on, you may need to implement features differently. For this, you can