🌱 fix readme links

[buhodev]

What this PR does / why we need it:

Fix the broken links on the README. Now all links point to the correct files/folders.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squash commits
• include documentation
• add unit tests

[janiskemper]

first link I clicked on was introduction and I got this: https://github.com/syself/cluster-api-provider-hetzner/blob/buho/fix-readme-links/docs/caph/01-getting-started/01-introduction

[buhodev]

first link I clicked on was introduction and I got this: https://github.com/syself/cluster-api-provider-hetzner/blob/buho/fix-readme-links/docs/caph/01-getting-started/01-introduction

It looks like github doesn't link to the proper file when not specifying the extension (.md). This works on vscode tho. I pushed a fix that adds the .md extension to (hopefully) all relative links in the docs. Now everyone should be able to click on any link here on github, their editor, or on the hosted website and don't get a 404.