Update README

Author: peter-evans

README.md

@@ -2,4 +2,30 @@
 
 A GitHub action to create an issue using content from a file.
 
-This is useful to pair with other actions that output to a file. This action can create an issue if a file exists at a specified path.
+This is useful to pair with other actions that output to a file. This action will create an issue if a file exists at a specified path. If the file does not exist the action exits silently.
+
+## Usage
+
+```hcl
+action "Create Issue From File" {
+  uses = "peter-evans/create-issue-from-file@v1.0.0"
+  secrets = ["GITHUB_TOKEN"]
+  env = {
+    ISSUE_TITLE = "An example issue"
+    ISSUE_CONTENT_FILEPATH = "./example-content/output.md"
+    ISSUE_LABELS = "report, automated issue"
+    ISSUE_ASSIGNEES = "peter-evans"
+  }
+}
+```
+
+#### Environment variables
+
+- `ISSUE_TITLE` (**required**) - A title for the issue
+- `ISSUE_CONTENT_FILEPATH` (**required**) - The file path to the issue content
+- `ISSUE_LABELS` - A comma separated list of labels to apply
+- `ISSUE_ASSIGNEES` - A comma separated list of assignees
+
+## License
+
+MIT License - see the [LICENSE](LICENSE) file for details