[doc] Extend README with v0.10.x and v1.x.x info

[heidemn]

Help admins to upgrade from legacy provider versions by specifying compatibility with Terraform versions.

Description

It was hard to find information about the compatibility of older Helm provider versions vs. Terraform versions. This makes it hard for admins to find out in which order the Helm provider and Terraform must be upgraded.

Therefore, I tested various combinations using terraform init to help others with outdated Terraform and/or provider versions. (I only tested Terraform >= v0.11.14, since I was assuming that nobody is using Terraform v0.10 any more.)

To make the information easily accessible, I chose to target the master branch, since this is what people will see when opening the repo. If you prefer, I could instead create similar PRs targeting release-0.10.x and release-1.x.x. (These branches are currently missing a "Requirements" section in the README.)

Acceptance tests

• [x] Have you added an acceptance test for the functionality being added? N/A - no functionality was added.

Release Note

Release note for CHANGELOG:

NONE

References

Related to https://github.com/hashicorp/terraform-provider-helm/issues/661

Community Note

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[hashicorp-cla]

All committers have signed the CLA.

[aareet]

Thanks for this @heidemn, this is useful info. I wonder if this is better formatted as a table/matrix to cover the different terraform versions. I'll discuss this idea with the team at our next triage meeting.

[heidemn]

@aareet sure, take your time 😄