Update registrierung-auf-der-openSenseMap.md

[synolus-david]

• include online compiling
• smaller fixes
• update screenshots

[synolus-david]

@bkari02 can you also completely delete Step 5 please?

• https://sensebox.github.io/books-v2/home/de/erste-schritte/verschluesselung.html

If its a lot of work ask @yhallowiegeht who just did that for another book.

[yhallowiegeht]

added into branches:

• typos&hotfixes_home and
• techbook will close the request