add - readme : possible error & bugfix

Author: Raphael Balet

README.md

@@ -11,6 +11,7 @@ Get the complete changelog here: https://github.com/rbalet/ngx-translate-multi-h
 
 * [Installation](#installation)
 * [Usage](#usage)
+* [Error & BugFix](#possible-error--bugfix)
 
 ## breaking change: v9.0.0
 * This library is now using `httpBackend` instead of the `httpClient`, to avoid being delayed by interceptor, which was creating errors while loading.
@@ -101,6 +102,22 @@ export function HttpLoaderFactory(_httpBackend: HttpBackend) {
 
 The loader will merge all translation files from the server using [deepmerge-ts](https://www.npmjs.com/package/deepmerge-ts).
 
+
+## Possible error & Bugfix
+### Can't resolve 'deepmerge-ts'
+1. run `npm i deepmerge-ts`
+
+This is due to some version of npm not being able to download peerDependencies properly.
+
+I decided to **not** move it under dependencies since it's considered to be a bad practice.
+
+### values.at is not a function
+1. Install `core-js`
+2. In `polyfills.ts`, add `import 'core-js/modules/es.array.at'`
+
+`deepmerge-ts@5` uses `Array.at`, which is [not supported](https://caniuse.com/?search=array.at) in _not so_ old versions of Safari `< 15.4`.
+
+
 ## Authors and acknowledgment
 * maintainer [Raphaël Balet](https://github.com/rbalet) 
 * Former maintainer [Dennis Keil](https://github.com/denniske)