Fix md formatting of exercises READMEs

[mao-sz]

Because

Consistent spacing, capitalisation and indentation. Prevents issues with some markdown parsers being stricter on the need for surrounding blank lines etc. (e.g. Okular - would render fenced code blocks incorrectly if not wrapped in blank lines).

This PR

• Uses consistent formatting for exercises' README.md

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the location of change: brief description of change format, e.g. 01_helloWorld: Update test cases
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If this PR includes any changes that affect the solution of an exercise, I've also updated the solution in the /solutions folder