Add section to README for how to install additional tools

.gitlab/README.md.template

@@ -181,6 +181,27 @@ Have a look at the individual template spec to learn about the available inputs.
 Have a look at the [`src/gitlab-tofu.sh`](src/gitlab-tofu.sh) script and how the `TF_`-prefixed
 variables are being used. You may set them according to your needs.
 
+### Install additional tools
+
+The `gitlab-opentofu` container image deliberately comes with minimal tooling
+to keep the image size small and be the least common denominator for our users.
+
+However, it is sometimes necessary to install additional tools. To do that you
+can overwrite the included jobs with a `before_script` entry. The `gitlab-opentofu`
+image uses `alpine` as its base image and therefore `apk` can be used to install
+the tools. For example to install `jq`:
+
+```yaml
+include:
+  - component: gitlab.com/components/opentofu/validate-plan@<VERSION>
+    inputs:
+      version: <VERSION>
+      opentofu_version: 1.6.1
+
+plan:
+  before_script:
+    - apk add jq
+```
 
 ## Releases & Versioning
 

README.md

@@ -202,6 +202,27 @@ The following OpenTofu versions are available with this component via the `opent
 Have a look at the [`src/gitlab-tofu.sh`](src/gitlab-tofu.sh) script and how the `TF_`-prefixed
 variables are being used. You may set them according to your needs.
 
+### Install additional tools
+
+The `gitlab-opentofu` container image deliberately comes with minimal tooling
+to keep the image size small and be the least common denominator for our users.
+
+However, it is sometimes necessary to install additional tools. To do that you
+can overwrite the included jobs with a `before_script` entry. The `gitlab-opentofu`
+image uses `alpine` as its base image and therefore `apk` can be used to install
+the tools. For example to install `jq`:
+
+```yaml
+include:
+  - component: gitlab.com/components/opentofu/validate-plan@<VERSION>
+    inputs:
+      version: <VERSION>
+      opentofu_version: 1.6.1
+
+plan:
+  before_script:
+    - apk add jq
+```
 
 ## Releases & Versioning