proposal: trim Docker documentation

[iuioiua]

I have no experience with Docker documentation, but I have some ideas of how it could be cleaned up:

• Remove:

  saaskit/README.md

  Line 33 in f2364de

  - [Docker](https://docs.docker.com/engine/install/)

• Create this file in the directory so the user doesn't have to:

  saaskit/README.md

  Lines 188 to 200 in f2364de

  	```docker
  	FROM denoland/deno:1.32.4
  	EXPOSE 8000
  	WORKDIR /app
  	ADD . /app
  	# Add dependencies to the container's Deno cache
  	RUN deno cache main.ts --import-map=import_map.json
  	CMD ["run", "--allow-run", "--allow-write", "--allow-read", "--allow-env", "--allow-net", "main.ts"]
  	```

• Ditto:

  saaskit/README.md

  Lines 202 to 210 in f2364de

  	Create a `.dockerignore` file in the root folder of your repo to make sure
  	certain files are not deployed to the docker container:
  	```
  	README.md
  	.example.env
  	.vscode/
  	.github/
  	```

• Ditto:

  saaskit/README.md

  Lines 212 to 232 in f2364de

  	A `docker-compose.yml` file will be needed to run the docker file on a VPS.
  	Here’s what that file in your repo's root folder will look like:
  	```yml
  	version: '3'
  	services:
  	web:
  	build: .
  	container_name: deno-sasskit
  	image: deno-image
  	environment:
  	- DENO_DEPLOYMENT_ID=${DENO_DEPLOYMENT_ID}
  	- GITHUB_CLIENT_ID=${GITHUB_CLIENT_ID}
  	- GITHUB_CLIENT_SECRET=${GITHUB_CLIENT_SECRET}
  	- STRIPE_SECRET_KEY=${STRIPE_SECRET_KEY}
  	- STRIPE_WEBHOOK_SECRET=${STRIPE_WEBHOOK_SECRET}
  	- STRIPE_PREMIUM_PLAN_PRICE_ID=${STRIPE_PREMIUM_PLAN_PRICE_ID}
  	ports:
  	- "8000:8000"
  	```

• Add a step number to each instruction, like other sections in the README.

Please correct me if I'm wrong on any of these.

[lambtron]

this makes sense to me. i can create a PR for it.

[iuioiua]

Some of this was done in #238.

[lambtron]

This PR addresses the remaining tasks in this issue: #253

[iuioiua]

This has been completed in #253.