Create Actions Walkthrough (#36)

* starting walkthrough docs

* versioning

docs/node12-action.md

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+# Creating a JavaScript Action
+
+The [node12-template](https://github.com/actions/node12-template) repo contains everything you need to get started.
+
+# Create a Repo from the Template
+
+Navigate to https://github.com/actions/node12-template
+
+Click on `Use this template` to create the repo for your action.
+
+![template](assets/node12-template.png)
+
+Complete creating your repo and clone the repo.
+
+> NOTE: The location of the repo will be how users will reference your action in their workflow file with the using keyword.
+
+e.g. To use https://github.com/actions/setup-node, user's will author:
+
+```yaml
+steps:
+    using: actions/setup-node@master
+```
+
+# Install Dependencies
+
+This will install the toolkit and other dependencies
+
+```bash
+$ npm install
+```
+
+The production dependencies are vendored into your action.  At runtime, the self contained action will be downloaded, extracted and run.
+
+# Define Metadata
+
+Your action has a name and a description.  Update the author.
+
+Create inputs that your unit of work will need.  These will be what workflow authors set with the `with:` keyword.
+
+```yaml
+name: 'My new action'
+description: 'A test action'
+author: 'GitHub'
+inputs: 
+  myInput:
+    description: 'Input to use'
+    default: 'world'
+runs:
+  using: 'node12'
+  main: 'lib/main.js'
+
+```
+
+Note that the action will be run with node 12 (carried by the runner) and the entry point is specified with `main:` 
+
+# Change Code and Add Tests
+
+The entry point is in main.ts
+
+```typescript
+import * as core from '@actions/core';
+
+async function run() {
+  try {
+    const myInput = core.getInput('myInput');
+    core.debug(`Hello ${myInput}!`);
+  } catch (error) {
+    core.setFailed(error.message);
+  }
+}
+
+run();
+```
+
+Modify tests in `__tests__\main.test.ts`.  The template uses [jest](https://github.com/facebook/jest).
+
+# Format the Code
+
+```bash
+$ npm run format
+```
+
+# Build and Test
+
+```bash
+$ npm run build
+
+> node12-template-action@0.0.0 build /Users/user/Projects/testnode12
+> tsc
+
+$ npm test
+
+> jest
+
+ PASS  __tests__/main.test.ts
+  TODO - Add a test suite
+    ✓ TODO - Add a test (1ms)
+
+Test Suites: 1 passed, 1 total
+...
+```
+
+# Commit and Push Changes
+
+```bash
+$ git add <whatever only files you added>
+$ git commit -m "Message"
+```
+
+> husky will add/vendor node_modules and prune dev dependencies.  See husky in package.json for details.  There is no need for you to add node_modules.
+
+# Publish Action
+
+Simply push your action to publish.
+
+```bash
+$ git push
+```
+
+> NOTE: Consider versioning your actions with tags.  See [versioning](docs/action-versioning.md)
+
+
+
+