Fix broken example script references in CLI README

[SarveshMahalingam]

This PR fixes incorrect relative links in tunix/cli/README.md that pointed to
non-existent example script paths.

The README previously referenced:

• examples/sft/mtnt
• examples/rl/gsm8k

Since README.md lives inside tunix/cli/, these links were incorrect.
They have been updated to the correct relative paths:

• ../../examples/sft/mtnt
• ../../examples/rl/gsm8k

This ensures the documentation accurately reflects the repository structure
and prevents broken links for users.

Checklist

• I have added all the necessary unit tests for my change.
• I have verified that my change does not break existing code and all unit tests pass.
• I have added all appropriate doc-strings/documentation.
• My PR is based on the latest changes of the main branch (if unsure, rebase the code).
• I have signed the Contributor License Agreement.
• I have followed Contribution Guidelines.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[selamw1]

Thanks! LGTM! Just a minor path fix below:

../../examples/rl/grpo/gsm8k

[SarveshMahalingam]

I've made the necessary modifications to the README file in the latest commit.Thank you!

LGTM