Build and attach acme.js to release (#55)

* Github action that runs when a release is created that builds acme.js and attaches it to the release.

* add instructions for downloading release

* simplify with gh command line; thanks @ryepup!

* README.md refinements

.github/workflows/release.yaml

@@ -0,0 +1,21 @@
+name: Upload acme.js to release page
+
+on:
+  release:
+    types: [created]
+
+jobs:
+  build:
+    name: Build release artifact
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Build dist/acme.js
+        run: make build
+
+      - name: Upload acme.js to release
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: gh release upload "${{ github.event.release.tag_name }}" ./dist/acme.js

README.md

@@ -15,12 +15,22 @@ NOTE: Some ACME providers have strict rate limits. Please consult with your prov
 ## Installation
 
 There are a few ways of using this repo. You can:
+* download `acme.js` from the latest [Release](https://github.com/nginx/njs-acme/releases)
 * build an ACME-enabled Docker image to replace your existing NGINX image
 * use Docker to build the `acme.js` file to use with your NGINX installation
 * build `acme.js` using a locally installed Node.js toolkit to use with your NGINX installation
 
 Each option above is detailed in each section below.
 
+### Downloading the Latest Release
+You can download the latest released `acme.js` file from the [Releases](https://github.com/nginx/njs-acme/releases) page. Typically you would place this in the path `/usr/lib/nginx/njs_modules/acme.js` in your NGINX server. See the example [nginx.conf](examples/nginx.conf) to see how to integrate it into your NGINX configuration.
+
+To integrate the downloaded `acme.js` file into a Docker image, you can add the following to your Dockerfile:
+```
+RUN mkdir -p /usr/lib/nginx/njs_modules/
+RUN curl -L -o /usr/lib/nginx/njs_modules/acme.js https://github.com/nginx/njs-acme/releases/download/v1.0.0/acme.js
+```
+
 ### Creating a Docker Image
 To create an Nginx+NJS+njs-acme Docker image, simply run:
 ```