Add some docs about which env vars are defined in new containers

@SvenDowideit FYI

Closes #3087

Signed-off-by: Doug Davis <dug@us.ibm.com>
Fix href in docs w.r.t. cgroups freezer pointer

Apparently, the [...] and (http...) need to be right after each other instead
of on different lines.

Signed-off-by: Doug Davis <dug@us.ibm.com>
Fix typo: reguardless should be regardless

Signed-off-by: Doug Davis <dug@us.ibm.com>
Add more info on attach inspired by discussion in #2855

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Add DOCKER_TLS_VERIFY environment variable, equivalent to --tlsverify flag

This makes it possible to make the Docker client "secure by default"
without wrapping the binary in a shell alias so that `--tlsverify` is
always passed.

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Merge pull request #8507 from duglin/Issue3087

Add some docs about which env vars are defined in new containers
Merge pull request #8524 from duglin/Regardless

Fix typo: reguardless should be regardless
Merge pull request #8523 from duglin/FixLinkCmdLine

Fix href in docs w.r.t. cgroups freezer pointer
Merge pull request #8435 from SvenDowideit/explain-docker-attach-more

Add more info on attach inspired by discussion in #2855
Merge pull request #8503 from aanand/tlsverify-environment-variable

Add DOCKER_TLS_VERIFY environment variable, equivalent to --tlsverify flag