Add Dockerfile for building the website (#699)

* Add Dockerfile for building the website

This Dockerfile was taken from spaCy.

* README: Remove command substitution in example

website/Dockerfile

@@ -0,0 +1,16 @@
+FROM node:11.15.0
+
+WORKDIR /thinc-io
+
+RUN npm install -g gatsby-cli@2.7.4
+
+COPY package.json .
+COPY package-lock.json .
+
+RUN npm install
+
+# This is so the installed node_modules will be up one directory
+# from where a user mounts files, so that they don't accidentally mount
+# their own node_modules from a different build
+# https://nodejs.org/api/modules.html#modules_loading_from_node_modules_folders
+WORKDIR /thinc-io/website/

website/README.md

@@ -14,6 +14,30 @@ npm run dev  # start dev server
 A `.prettierrc` is included in the repo, so if you set up auto-formatting with
 Prettier, it should match the style.
 
+## Build and run the website in a Docker container
+
+Rather than installing NPM locally, you can also build a Docker container with
+the prerequisite dependencies:
+
+```bash
+docker build -t thinc-io .
+```
+
+Afterwards, the website can be built and run in the container:
+
+```bash
+docker run --rm -it \
+  -v $PWD:/thinc-io/website \
+  -p 8000:8000 \
+  thinc-io \
+  gatsby develop -H 0.0.0.0
+```
+
+This is currently the only way to build the website on ARM64 Macs, since the
+required Node.js version is not built for macOS/ARM64.
+
+These commands also work with Podman by replacing `docker` by `podman`.
+
 ## Directory structure
 
 - `/docs`: Docs pages as Markdown.