chore(litserve): added RAG deployment example in readme

[patchy631]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Adds a readme example for deploying RAG using LitServe

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in GitHub issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82%. Comparing base (6c49137) to head (4d036ca).
Report is 2 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #231   +/-   ##
===================================
  Coverage    81%    82%           
===================================
  Files        13     13           
  Lines      1036   1044    +8     
===================================
+ Hits        842    853   +11     
+ Misses      194    191    -3     

[aniketmaurya]

LGTM!