docs: Add message for OpenTofu support

[CHERIANS]

Purpose

Added message in Readme for mentioning OpenTofu support

• ...

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce? [ ] Bugfix [ ] Feature [ ] Refactoring (no functional changes, no api changes) [x] Documentation content changes [ ] Other... Please describe:

How to Test

NA

What to Check

Very the OpenTofu Compatibility section in Readme.md

• Automated tests are executed successfully

NA

Other Information

NA

Checklist for reviewer

The following organizational tasks must be completed before merging this PR:

• [X] The PR is assigned to the Terraform project and a status is set (typically "in review").
• [X] The PR has the matching labels assigned to it.
• [X] The PR has a milestone assigned to it.
• [X] If the PR closes an issue, the issue is referenced.
• [X] Possible follow-up items are created and linked.

[lechnerc77]

Just change of README.md - no build checks needed