Update README

Author: peter-evans

README.md

@@ -81,7 +81,7 @@ To use this strategy, set `BRANCH_SUFFIX` to the value `none`. The variable `PUL
 
 If there are files or directories you want to ignore you can simply add them to a `.gitignore` file at the root of your repository. The action will respect this file.
 
-## Example
+## Examples
 
 Here is an example that sets all the main environment variables.
 
@@ -102,10 +102,10 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           COMMIT_MESSAGE: Add report file
+          PULL_REQUEST_TITLE: '[Example] Add report file'
           PULL_REQUEST_BODY: >
             This PR is auto-generated by 
             [create-pull-request](https://github.com/peter-evans/create-pull-request).
-          PULL_REQUEST_TITLE: '[Example] Add report file'
           PULL_REQUEST_LABELS: report, automated pr
           PULL_REQUEST_ASSIGNEES: peter-evans
           PULL_REQUEST_REVIEWERS: peter-evans
@@ -120,6 +120,41 @@ This configuration will create pull requests that look like this:
 
 ![Pull Request Example](https://github.com/peter-evans/create-pull-request/blob/master/pull-request-example.png?raw=true)
 
+### Dynamic configuration using variables
+
+The following examples show how configuration for the action can be dynamically defined in a previous workflow step.
+
+The recommended method is to use `set-output`. Note that the step where output variables are defined must have an id.
+
+```yml
+      - name: Set output variables
+        id: vars
+        run: |
+          echo ::set-output name=pr_title::"[Test] Add report file $(date +%d-%m-%Y)"
+          echo ::set-output name=pr_body::"This PR was auto-generated on $(date +%d-%m-%Y) \
+            by [create-pull-request](https://github.com/peter-evans/create-pull-request)."
+      - name: Create Pull Request
+        uses: peter-evans/[email protected]
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PULL_REQUEST_TITLE: ${{ steps.vars.outputs.pr_title }}
+          PULL_REQUEST_BODY: ${{ steps.vars.outputs.pr_body }}
+```
+
+Since the action reads environment variables from the system, it's technically not necessary to explicitly pass them as long as they exist in the environment. So the following method using `set-env` *also* works, but explicitly passing the configuration parameters using the previous method is perferred for its clarity.
+
+```yml
+      - name: Set environment variables
+        run: |
+          echo ::set-env name=PULL_REQUEST_TITLE::"[Test] Add report file $(date +%d-%m-%Y)"
+          echo ::set-env name=PULL_REQUEST_BODY::"This PR was auto-generated on $(date +%d-%m-%Y) \
+            by [create-pull-request](https://github.com/peter-evans/create-pull-request)."
+      - name: Create Pull Request
+        uses: peter-evans/[email protected]
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+```
+
 ## License
 
 [MIT](LICENSE)