Documentation section on the escape character needs an update

File: engine/reference/builder.md

Hi!

I believe the section https://docs.docker.com/engine/reference/builder/#escape is outdated and should be rewritten.

First, microsoft/nanoserver is not maintained anymore, so running FROM microsoft/nanoserver [implicit tag: latest] will output an error. But most importantly, I couldn't reproduce the COPY testfile.txt c:\\ bug mentioned there, this has probably been fixed already. I only get a weird bug if I run RUN dir c:\\, which is absent if RUN dir c:\somedir\\ is run instead.

I'd like to ask one of the mods/people in charge to please update this section, so other users don't waste time trying to figure out how to escape the "escape character". I think it can always be escaped by using it twice (for example: \\), except in RUN or CMD instructions

Thanks

Start with engine/reference/builder.md and read the #escape section alongside its documented examples. Reproduce the microsoft/nanoserver and COPY or RUN cases with current Docker behavior, then update the section so it describes only verified behavior and current image references.