Howto doc for manually adding routing tiles

[stanw-cg]

Howto doc for manually adding routing tiles and the basic information for routing tiles.

[treee111]

thanks for the howto-doc @stanw-cg!
Very detailed and understandable :-)

I added some comments to make it better readable directly on Github.
It would be great if you integrate them.
If you don't have time or don't like to, I could also do that!

[stanw-cg]

Thanks! Let me update the doc.

[stanw-cg]

@treee111 Sorry for the multiple commits due to not familiar with markdown syntax :) Please help to review and let me know if further changes are required. Thanks!

[treee111]

Hi @stanw-cg, don't worry about the commits! Later on we can stash all your commits into one! 👍

There is also a Plugin to preview Markdown in VSCode (or maybe also another editor you use): https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one

[treee111]

thanks for updating everything, great work @stanw-cg!
It looks fine in my opinion.

If you are also satisfied, I gonna merge that PR?

[stanw-cg]

@treee111 Thanks a lot!