Update README with usage instructions (#11)

This change adds usage for users that outlines the workflow example and all the available inputs.

README.md

@@ -1,2 +1,42 @@
-# bandit-action
-GitHub Action for Bandit
+# Bandit by PyCQA
+
+The official [Bandit](https://github.com/PyCQA/bandit) Action developed by the [PyCQA](https://github.com/PyCQA).
+
+## Usage
+
+Here is a minimal complete example workflow to create a Code Scanning action using Bandit.
+
+```yaml
+name: Bandit
+
+on:
+  workflow_dispatch:
+
+jobs:
+  analyze:
+    runs-on: ubuntu-latest
+    permissions:
+      # required for all workflows
+      security-events: write
+      # only required for workflows in private repositories
+      actions: read
+      contents: read
+    steps:
+      - name: Perform Bandit Analysis
+        uses: PyCQA/bandit-action@v1
+```
+
+## Inputs
+
+| Name | Description | Required | Default Value |
+|--|--|--|--|
+| configfile | Config file to use for selecting plugins and overriding defaults | False | `"DEFAULT"` |
+| profile | Profile to use (defaults to executing all tests) | False | `"DEFAULT"` |
+| tests | Comma-separated list of test IDs to run | False | `"DEFAULT"` |
+| skips | Comma-separated list of test IDs to skip | False | `"DEFAULT"` |
+| severity |Report only issues of a given severity level or higher. "all" and "low" are likely to produce the same results, but it is possible for rules to be undefined which will not be listed in "low". Options include: {all, high, medium, low} | False | `"DEFAULT"` |
+| confidence | Report only issues of a given confidence level or higher. "all" and "low" are likely to produce the same results, but it is possible for rules to be undefined which will not be listed in "low". Options include: {all, high, medium, low} | False | `"DEFAULT"` |
+| exclude | Comma-separated list of paths (glob patterns supported) to exclude from scan (note that these are in addition to the excluded paths provided in the config file) | False | `".svn,CVS,.bzr,.hg,.git,__pycache__,.tox,.eggs,*.egg"` |
+| baseline | Path of a baseline report to compare against (only JSON-formatted files are accepted) | False | `"DEFAULT"` |
+| ini | Path to a .bandit file that supplies command line arguments | False | `"DEFAULT"` |
+| targets | Source file(s) or directory(s) to be tested | False | `"."` |