Add documentation for 16.0 usermod system

docs/advanced/community-usermods.md

@@ -0,0 +1,26 @@
+---
+title: Community Usermods
+---
+
+This page is an index of usermods written by the WLED community. Entries are maintained by their authors; the WLED project does not test or endorse them.
+
+To help people find your usermod even before it appears here, tag your GitHub repository with the [`wled-usermod`](https://github.com/topics/wled-usermod) topic.
+
+## Adding your usermod
+
+Open a pull request to [WLED-Docs](https://github.com/wled/WLED-Docs) adding a row to the table below. One row, one PR.
+
+Use this format:
+
+```markdown
+| [Name](https://github.com/you/your-usermod) | Short description | @yourname | esp32 |  |
+```
+
+Platforms: `esp32`, `esp8266`, or `both`.
+
+## Index
+
+| Name | Description | Author | Platforms | Notes |
+|---|---|---|---|---|
+| [wled-usermod-example](https://github.com/wled/wled-usermod-example) | Annotated template — fork this to start your own usermod | @wled | both | Official starting point |
+| [user_fx](https://github.com/wled/WLED/tree/main/usermods/user_fx) | Community effects usermod — add your own effects here or use as a template | @wled | both | Ships with WLED; enable with `custom_usermods = user_fx` |

docs/advanced/compiling-wled.md

@@ -75,6 +75,20 @@ Once you've confirmed VSCode with Platformio is set up correctly, you can add/de
  7. Put your `-D` overrides on this new line, giving each `-D` it's own new line.
  8. Compile your freshly customized WLED image!
 
+### Adding usermods
+
+To include one or more usermods in your build, add a `custom_usermods` line to your environment in `platformio_override.ini`:
+
+```ini
+[env:esp32dev_temperature]
+extends = env:esp32dev
+custom_usermods =
+  audioreactive
+  Temperature
+```
+
+Each name corresponds to a folder under `usermods/`. No other file editing is required — usermods self-register when compiled in. For full details, including how to add external usermods from a git repository and how to write your own, see [Custom Features](/advanced/custom-features).
+
 ### Flashing the compiled binary
 
 !!! tip