[ZENTORCH INFRA] Add git checkout statement in README.md

-- Add `git checkout r4.2` in README.md

Signed-off-by: Venkata Durga Rao <[email protected]>
Change-Id: I285ca3eeec852af8925c6682fa33b53acc84fe6c
(cherry picked from commit 4b7cfd7)

Author: Venkata-Durga-Rao

README.md

@@ -138,6 +138,10 @@ Run the following commands:
 git clone "ssh://gerritgit/amd/ec/ZenDNN_PyTorch_Plugin"
 cd ZenDNN_PyTorch_Plugin/
 ```
+>Note: Repository defaults to master branch, to build the version 4.2 checkout the branch r4.2.
+```bash
+git checkout r4.2
+```
 
 ### 2.2.1. Preparing third party repositories