website: Document TF_PLUGIN_CACHE_MAY_BREAK_DEPENDENCY_LOCK_FILE env var

This is an alternative way to set the CLI configuration setting
plugin_cache_may_break_dependency_lock_file to activate the transitional
compatibility behavior that prefers to break the dependency lock file if
that would create an additional opportunity to use the plugin cache.

website/docs/cli/config/config-file.mdx

@@ -387,7 +387,7 @@ grow to contain several unused versions which you must delete manually.
 safe. The provider installer's behavior in environments with multiple `terraform
 init` calls is undefined.
 
-## Allowing the Provider Plugin Cache to break the dependency lock file
+### Allowing the Provider Plugin Cache to break the dependency lock file
 
 ~> **Note:** The option described in is for unusual and exceptional situations
 only. Do not set this option unless you are sure you need it and you fully
@@ -415,6 +415,10 @@ to confirm it:
 plugin_cache_may_break_dependency_lock_file = true
 ```
 
+Alternatively, you can set the environment variable
+`TF_PLUGIN_CACHE_MAY_BREAK_DEPENDENCY_LOCK_FILE` to any value other than the
+empty string or `0`, which is equivalent to the above setting.
+
 Setting this option gives Terraform CLI permission to create an incomplete
 dependency lock file entry for a provider if that would allow Terraform to
 use the cache to install that provider. In that situation the dependency lock

website/docs/cli/config/environment-variables.mdx

@@ -151,6 +151,12 @@ The location of the [Terraform CLI configuration file](/terraform/cli/config/con
 export TF_CLI_CONFIG_FILE="$HOME/.terraformrc-custom"
 ```
 
+## TF_PLUGIN_CACHE_DIR
+
+The `TF_PLUGIN_CACHE_DIR` environment variable is an alternative way to set [the `plugin_cache_dir` setting in the CLI configuration](/terraform/cli/config/config-file#provider-plugin-cache).
+
+You can also use `TF_PLUGIN_CACHE_MAY_BREAK_DEPENDENCY_LOCK_FILE` to activate [the transitional compatibility setting `plugin_cache_may_break_dependency_lock_file`](/terraform/cli/config/config-file#allowing-the-provider-plugin-cache-to-break-the-dependency-lock-file).
+
 ## TF_IGNORE
 
 If `TF_IGNORE` is set to "trace", Terraform will output debug messages to display ignored files and folders. This is useful when debugging large repositories with `.terraformignore` files.