Add OpenTofu min supported version to readme

[swade1987]

Description

I have manually validated the examples work with OpenTofu version 1.7.0 (latest)

Motivation and Context

Fixes #683

How has this been tested?

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

$ make testacc

...

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Documentation

• I have updated the documentation (if required) with make docs

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s

Community Note

• Please vote on this issue by adding a 👍 reaction to the original issue to help the community and maintainers prioritise this request
• If you are interested in working on this issue or have submitted a pull request, please leave a comment

[stefanprodan]

Please rename the commit to the PR title and remove all changes except for the readme ones.

[swade1987]

Can I propose we leave the CI job name changes as they are pretty useful.

[stefanprodan]

Can I propose we leave the CI job name changes as they are pretty useful.

But they are not related to OpenTofu, let's keep this PR scoped to what it suppose to do.