Improve useability of HOWTO examples

[patcon]

Right now, in the HOWTO.md doc, we have some expandable config examples:
https://github.com/g0v-network/domains/blob/main/docs/HOWTO.md#examples

Right now, these look like this (using the diff formatter):

It's nice, because one diff can show changes in multiple files in the repo.

But as you can see in the above screenshot, highlighting also includes the + and - context lines.

It would be nice if there was a quicker, easier way to create a new PR. This could involve one or both of:

1. Creating a hyperlink that initiates a stub PR and scaffolds out a new file, like Hypha does in the right-hand column of their meeting note directory.

2. Use GitHub flavoured markdown to make the diffs more selectable using GitHub's permalink embed style. This is commonly used in pull requests and issues, but also works in any markdown docs within the repo. Example: https://github.com/patcon/test-github-markdown/

   domains/c4nada.ca.domain/c4nada.ca.yaml

   Lines 1 to 10 in 1601c05

   	---
   	'':
   	- type: TXT
   	values:
   	# Who has admin for this domain
   	- admin=patcon
   	# Used for 301 redirect service below
   	- 301 https://g0v.tw/
   	- type: ALIAS
   	value: 301.ronny.tw.

cc: Sam @therealitycorp