Update readme with usage

Author: will-molloy

README.md

@@ -1,3 +1,30 @@
 # copybara-action
 
-GitHub Action that runs [Copybara](https://github.com/google/copybara)
+Runs [Copybara](https://github.com/google/copybara) in GitHub Actions
+
+## Usage
+Specify `wilmol/copybara-action@v1` as a `step` in your `workflow.yml` file, for example:
+```
+steps:
+  - uses: actions/checkout@v1
+
+  - uses: wilmol/copybara-action@v1
+    with:
+      git_name: wilmol
+      git_email: willjoemolloy@gmail.com
+      ssh_key: ${{ secrets.SSH_KEY }}
+      ssh_known_hosts: ${{ secrets.KNOWN_HOSTS }}
+```
+
+__Note,__ internally the action runs docker (specifically [this image](https://hub.docker.com/r/sharelatex/copybara)) so the step must run on Linux.
+
+## Arguments
+| Input  | Description | Usage |
+| :---:     |     :---:   |    :---:   |
+| `git_name` | git config username, for authoring with Copybara | _required_ |
+| `git_email` | git config email, for authoring with Copybara | _required_ |
+| `ssh_key` | ssh public key, for authenticating with Copybara | _required_ |
+| `ssh_known_hosts` | ssh known hosts file contents, for authenticating with Copybara | _required_ |
+| `path` | `copy.bara.sky` file path | optional (defaults to repo root) |
+
+See https://github.com/google/copybara for more details, specifically [Using Docker to build and run Copybara](https://github.com/google/copybara#using-docker-to-build-and-run-copybara). 

action.yml

@@ -1,22 +1,22 @@
-name: "Copybara"
-description: "GitHub Action that runs Copybara"
-author: "Will Molloy <willjoemolloy@gmail.com>"
+name: "copybara-action"
+description: "Runs Copybara in GitHub Actions"
+author: "Will Molloy <willjoemolloy@gmail.com> & Ji Paik <jjeonie@gmail.com>"
 
 inputs:
   git_name:
-    description: "Name to use when authoring commits"
+    description: "git config username, for authoring with Copybara"
     required: true
   git_email:
-    description: "Email address to use when authoring commits"
+    description: "git config email, for authoring with Copybara"
     required: true
   ssh_key:
-    description: "SSH public key for authenticating with the destination repository"
+    description: "ssh public key, for authenticating with Copybara"
     required: true
   ssh_known_hosts:
-    description: "SSH known hosts file contents with the destination repository's fingerprint"
+    description: "ssh known hosts file contents, for authenticating with Copybara"
     required: true
   path:
-    description: "Path to copy.bara.sky"
+    description: "copy.bara.sky file path"
     required: false
     default: "."