Update docker.md to prevent #2836 on windows

[stefanseeger]

On windows git is converting the line ending LF per default to CRLF, which will break the docker compose see #2836
To enforce git clone with line ending lf I updated the docker.md

[stefanseeger]

Hi @mashb1t ,
I just found that it might be a better solution to add a .gitattributes file enforcing the line endings for everyone using this repo.
See docs: https://docs.github.com/en/get-started/getting-started-with-git/configuring-git-to-handle-line-endings
What do you think about it?

[mashb1t]

@stefanseeger yes, sounds reasonable. Please go ahead and add the file, if not i can also do it.

[mashb1t]

done in #2991

[stefanseeger]

@stefanseeger yes, sounds reasonable. Please go ahead and add the file, if not i can also do it.

You are too quick, thank you!