docs(README): add note about patching

Author: buschtoens

src/README.md

@@ -26,3 +26,15 @@ For addons & engines:
 ```bash
 ember install -S ember-auto-import ember-auto-import-typescript
 ```
+
+### Patching
+
+This addon requires
+[PR #249 "feat(splitter): add `.ts` extension to resolver"][pr-249]. There's not
+been a new release since the PR got merged. This means you need to patch
+ember-auto-import yourself. I suggest to use [`patch-package`][patch-package]
+with the [`ember-auto-import+1.5.2.patch`][patch-file].
+
+[pr-249]: https://github.com/ef4/ember-auto-import/pull/249
+[patch-package]: https://github.com/ds300/patch-package#readme
+[patch-file]: /patches/ember-auto-import+1.5.2.patch