chore(readme): add info on linting other file types (#1188)

* Update README: info on linting other file types

* chore: Update README.md

Co-authored-by: Sky Higgins <eveningsky@gmail.com>

* chore: fix line length

Co-authored-by: Tony Brix <tony@brix.ninja>
Co-authored-by: Sky Higgins <eveningsky@gmail.com>

Author: 3 people

README.md

@@ -27,6 +27,11 @@ installed
 for you. If you are using an alternative `linter-*` consumer, 
 the `linter` package can be disabled.
 
+If you wish to lint files in JavaScript-derivative languages (like Typescript,
+Flow) with ESLint, you must add the scope name for that grammar to the
+`List of scopes to run ESLint on` option in `linter-eslint` Settings. For
+example, to lint TypeScript files, add `source.ts` to the list.
+
 ## Use with plugins
 
 You have two options: