[Ixia] Added README file for contributor info to ixia dir (#7987)

* new README file for contributor info to ixia directory

* fixed pre commit check

* Update README.md

* Update README.md

tests/ixia/README.md

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+# Important Note for Contributors
+
+Test cases in this directory have been migrated to /tests/snappi. **Since December 2022, Snappi has become our primary API (through `snappi`) for interacting with hardware traffic generators**, while we are deprecating the existing `ixia` API from our test repository. Any new test cases from contributors requiring the use of any *hardware traffic generators* should utilise the `snappi` API, and any new pull requests which still calls the `ixia` API will be disregarded.
+
+You can find more information on the `snappi` API such as its usage [here](https://github.com/open-traffic-generator/snappi-ixnetwork) or by viewing the code in the [tests/snappi](https://github.com/sonic-net/sonic-mgmt/tree/master/tests/snappi) directory of this repository.