Document which files the language client should watch (#11)

readme.md

@@ -53,6 +53,20 @@ are supported.
 
 `remark-language-server` uses the same configuration files as
 [`remark-cli`][remark-cli].
+These files are:
+
+*   `.remarkrc`
+*   `.remarkrc.cjs`
+*   `.remarkrc.js`
+*   `.remarkrc.json`
+*   `.remarkrc.mjs`
+*   `.remarkrc.yaml`
+*   `.remarkrc.yml`
+*   `package.json`
+
+Language clients should notify the language server if these files change.
+They are looked up starting at the folder where the checked markdown file
+exists.
 
 ## Examples