add checks documentation

Author: GrantBirki

docs/assets/required-ci-checks-example.png

@@ -1 +1,54 @@
 # Checks ✅
+
+> This feature was originally requested via [#73](https://github.com/github/branch-deploy/issues/73)
+
+The branch-deploy Action contains a useful input option to help give developers more control over how CI checks are handled during the deployment process. Some teams may have very strict controls over deployments and require **all status checks** to pass before a deployment can start. In this case, all CI checks must pass and that includes required, or non-required checks. Other teams may have a more relaxed approach and only require certain checks to pass before a deployment can start. This is where the `checks` input option comes in handy.
+
+## Required CI Checks
+
+First, let's explain what a "required" CI check is in case you're not familiar. A required CI check is a check that must pass before a pull request can be merged. This is a setting that can be configured in the repository settings under the "Branches" section. This section is shown in the screenshot below:
+
+![required-ci-checks](assets/required-ci-checks.png)
+
+> This example came directly from this respository's settings
+
+So in this particular repository, the following CI checks are required:
+
+- `test`
+- `package-check`
+- `lint`
+- `actions-config-validation`
+
+Any other CI checks that run on a pull request are not required and are considered non-required checks.
+
+## Using the `checks` Input Option
+
+This section will contain a few examples of how you can use the `checks` option
+
+### Example 1: All CI Checks Must Pass
+
+This example shows how you can use the `checks` option to require all CI checks to pass before a deployment can start. This is the **default** behavior of the Action if you do not specify the `checks` option.
+
+```yaml
+- name: branch-deploy
+  uses: github/branch-deploy@vX.X.X # replace with the latest version of this Action
+  id: branch-deploy
+  with:
+    checks: "all" # all CI checks (required or not) must pass before a deployment can start
+```
+
+### Example 2: Only Required CI Checks Must Pass
+
+This example shows how you can use the `checks` option to require only the **required** CI checks to pass before a deployment can start. This is useful if you have non-required checks that you don't want to block a deployment.
+
+```yaml
+- name: branch-deploy
+  uses: github/branch-deploy@vX.X.X # replace with the latest version of this Action
+  id: branch-deploy
+  with:
+    checks: "required" # only required CI checks must pass before a deployment can start
+```
+
+The screenshot below demonstrates how this option works in a real-world scenario. You can see how there are two CI checks defined on the pull request. One is called `test1` which is **required** and **passing**. The other is called `test2` which is **not required** and **failing**. Since the `checks` option is set to `required`, the deployment will start because the required check is passing and is the only status check taken into consideration for a deployment.
+
+![required-ci-checks-example](assets/required-ci-checks-example.png)