Add CLA badge (#1523)

## Description:

Add CLA badge to README

## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [ ] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [ ] I have added relevant tests to the test directory
- [ ] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [ ] I have read and accepted the CLA aggreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

README.md

@@ -12,6 +12,7 @@ This is a fork/rewrite of WarFront.io. Credit to https://github.com/WarFrontIO.
 
 ![CI](https://github.com/openfrontio/OpenFrontIO/actions/workflows/ci.yml/badge.svg)
 [![Crowdin](https://badges.crowdin.net/openfront-mls/localized.svg)](https://crowdin.com/project/openfront-mls)
+[![CLA assistant](https://cla-assistant.io/readme/badge/openfrontio/OpenFrontIO)](https://cla-assistant.io/openfrontio/OpenFrontIO)
 
 # OpenFront - Licensing