Small additions to the plugins guide in the docs see #50

Author: semohr

docs/plugins.md

@@ -8,11 +8,12 @@ Plugin support is experimental.
 Installing beets plugins varies depending on the particular plugin.
 [See the official docs](https://docs.beets.io/en/latest/plugins/index.html).
 
-We might automate this in the future, but for now you can place either a `requirements.txt` or `startup.sh` in the `/config` folder.
-After starting, the container will run the startup script if it exists, and afterwards install the requirements from the `requirements.txt` file using pip.
+We might automate this in the future, but for now you can place a `requirements.txt` and/or `startup.sh` in the `/config` folder. The `requirements.txt` may include [python dependencies](https://pip.pypa.io/en/stable/reference/requirements-file-format/), and the `startup.sh` file may be an executable shell script that is compatible with the container's alpine linux base.
 
+On startup, the container will run the startup script if it exists, and afterwards install the requirements from the `requirements.txt` file using pip.
 
 ## Example startup.sh: keyfinder
+
 For example, we can install the [keyfinder plugin](https://docs.beets.io/en/latest/plugins/keyfinder.html) via `startup.sh`, as  it requires quite a few build steps.
 
 Place the following in a `startup.sh` file in the `/config` folder.