Rewrote the ENTRYPOINT section in builder

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
add missing docs for rm

Docker-DCO-1.1-Signed-off-by: Adrien Folie <folie.adrien@gmail.com> (github: folieadrien)
Merge pull request #6988 from jamtur01/entry

Rewrote the ENTRYPOINT section in builder
Merge pull request #6990 from folieadrien/missing-rm-api-docs

add missing api docs for #6863
General cleanup of the builder.md file

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)