noUnusedParameters: add note about underscore prefix exception (#3178)

Co-authored-by: Jake Bailey <5341706+jakebailey@users.noreply.github.com>

Author: jamonholmgren

packages/tsconfig-reference/copy/en/options/noUnusedParameters.md

@@ -13,3 +13,12 @@ const createDefaultKeyboard = (modelID: number) => {
   return { type: "keyboard", modelID: defaultModelID };
 };
 ```
+
+Parameters declaration with names starting with an underscore (`_`) are exempt from the unused parameter checking. e.g.:
+
+```ts twoslash
+// @noUnusedParameters
+const createDefaultKeyboard = (_modelID: number) => {
+  return { type: "keyboard" };
+};
+```