docs: Document that __GIT_WORKING_DIR__ available for `terraform_tr…

…ivy` (#654)

README.md

@@ -883,6 +883,14 @@ To replicate functionality in `terraform_docs` hook:
  - --args=--skip-dirs="**/.terraform"
  ```
 
+4. When you have multiple directories and want to run `trivy` in all of them and share a single config file - use the `__GIT_WORKING_DIR__` placeholder. It will be replaced by `terraform_trivy` hooks with Git working directory (repo root) at run time. For example:
+
+ ```yaml
+ - id: terraform_trivy
+ args:
+ - --args=--ignorefile=__GIT_WORKING_DIR__/.trivyignore
+ ```
+
 ### terraform_validate
 
 > [!IMPORTANT]