Updates README

[matsduf]

Purpose

This PR

• Removes detaild Docker build instructions.
• Adds referral to Docker build documentation.
• Moves links setting to end of document.
• Break long lines.
• Adds editorial updates.

The updated document has a link to a document that exists in develop branch only. The link is on purpose to the master branch, where the document will be available after release.

https://github.com/zonemaster/zonemaster/blob/master/docs/internal-documentation/maintenance/ReleaseProcess-create-docker-image.md

The updated document has a link to a document that has been updated in the develop branch. The link is on purpose to the master branch, where the document will be available after release.

https://github.com/zonemaster/zonemaster-cli/blob/master/USING.md

Changes

Updates README.md

How to test this PR

Documentation only.

[matsduf]

@pnax and @blacksponge, can you review?