Add support for OpenTofu v1.6

Most of the work on OpenTofu support has already been done in #164.
The last piece is running CI on the GA version and clarifying in the
description that OpenTofu is supported.

.github/workflows/test.yaml

@@ -65,7 +65,7 @@ jobs:
       fail-fast: false
       matrix:
         opentofu:
-        - 1.6.0-alpha5
+        - 1.6.0
     env:
       OPENTOFU_VERSION: ${{ matrix.opentofu }}
       TFMIGRATE_EXEC_PATH: tofu

.goreleaser.yml

@@ -28,7 +28,7 @@ brews:
       name: "Masayuki Morita"
       email: minamijoyo@gmail.com
     homepage: https://github.com/minamijoyo/tfmigrate
-    description: "A Terraform state migration tool for GitOps"
+    description: "A Terraform / OpenTofu state migration tool for GitOps"
     skip_upload: auto
     test: |
       system "#{bin}/tfmigrate -v"

README.md

@@ -3,7 +3,7 @@
 [![GitHub release](https://img.shields.io/github/release/minamijoyo/tfmigrate.svg)](https://github.com/minamijoyo/tfmigrate/releases/latest)
 [![GoDoc](https://godoc.org/github.com/minamijoyo/tfmigrate/tfmigrate?status.svg)](https://godoc.org/github.com/minamijoyo/tfmigrate)
 
-A Terraform state migration tool for GitOps.
+A Terraform / OpenTofu state migration tool for GitOps.
 
 ## Table of content
 <!--ts-->
@@ -81,9 +81,17 @@ This brings us to a new paradigm, that is to say, Terraform state operation as C
 
 ## Requirements
 
-The tfmigrate invokes `terraform` command under the hood. This is because we want to support multiple terraform versions in a stable way.
+The tfmigrate invokes `terraform` or `tofu` command under the hood. This is because we want to support multiple Terraform / OpenTofu versions in a stable way.
 
-The minimum requirement is Terraform v0.12 or higher, but we recommend the Terraform v1.x.
+### Terraform
+
+The minimum required version is Terraform v0.12 or higher, but we recommend the Terraform v1.x.
+
+### OpenTofu
+
+If you want to use OpenTofu, a community fork of Terraform, you need to set the environment variable `TFMIGRATE_EXEC_PATH` to `tofu`.
+
+The minimum required version is OpenTofu v1.6 or higher.
 
 ## Getting Started