[DOCS] Update README.md

[alexander-nitsche]

• move "Verified extension" status to own badge to align it with similar status information
• add table with links in prominent place to guide reader to next steps (full documentation and installation)
• use common title pattern "TYPO3 extension " to make the context of this application clear at first glance

Related: https://github.com/TYPO3-Documentation/T3DocTeam/issues/182

[alexander-nitsche]

hi Nikita, hi Mask team,

i just came across your extension documentation while having a look at intercept. this pr is to align with similar documentations, that want to improve the guiding of the user. it provides him or her with all required information, especially with links to the next steps like installation and full documentation.

i further aligned the title to similar ones and moved the "Verified extension" status to an own badge, to inform the reader immediately about the scope and to bring as much information as possible to the first section of the page.

some questions remain:

1. consider to move all documentation below the new links table into the full documentation, as having all documentation in one place only eases maintenance for the author and orientation for the reader.
2. you might want to add the project homepage to the table of links, but i was not sure, if that page is still actively maintained. if so, an entry | Homepage | https://mask.webprofil.at/ | would be in line with other READMEs.

great work though!