Restructure README installation & configuration instructions.

[joohoi]

Readme should get restructured:

• The DNS configuration and Testing it out - sections should follow the Install section.
• Troubleshooting section should get added after Testing it out - section.
• Different sections should be linked to from the top of the README for easier access.

[werty1st]

i spent a few hours on this but didnt get it to work. i tried the docker container but it didnt create the requested txt records. i dont want to go into details but just vote for "better" documentation/instructions.