Updated references from akka to pekko #28

[samikrc]

Updated three markdown files:

• CONTRIBUTING.md
• README.md
• RELEASING.md

[pjfanning]

There was an existing PR that was approved and is now merged - #33.

It is worth checking to see what other issues and PRs are open before proceeding with new PRs.

Could you rebase your changes and look at PR comments?

[pjfanning]

@samikrc I hope you don't mind but I resolved the merge conflicts myself. Would you be still able to make the rest of the requested changes?

[samikrc]

Hi @pjfanning : thanks for the review. I have incorporated all the comments. Please review.

[samikrc]

Hello @pjfanning @Claudenw : I have not seen any new comment in last couple of days and the PR is ready. Can this be merged? Thanks!
@Claudenw : Can #28 be assigned to me?

[pjfanning]

thanks @samikrc - I'll merge as is - it is good to lower the Akka specific references in the docs - any remaining issues can be resolved in new PRs