Added bitbucket hook info and warning re: validating accounts.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
Edits based on feedback from docs team.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
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)
Merge pull request #6989 from jamtur01/builder

General cleanup of the builder.md file
Merge pull request #6967 from fredlf/copyedit-builds

Added bitbucket hook info and warning re: validating accounts.