docs: improve documentation for `docker commit --change`

Problem description

Syntax for commit --change should be further elaborated in regard to setting the Env value. The example given works for setting one Env environment variable, though it seems to be additive only. Can one set multiple Env variables? Can one delete an Env variable? Can one completely overwrite all of Env? In addition, another syntax seems to work that includes square brackets. See http://stackoverflow.com/questions/29015023/docker-commit-created-images-and-entrypoint and the answer by user: sxc731. This syntax could be elaborated upon, unless using it is not best practice.

Problem location

• I saw a problem on the following URL: https://docs.docker.com/engine/reference/commandline/commit/

https://docs.docker.com/engine/reference/commandline/commit/
Aparently this references:
https://github.com/docker/cli/blob/master/docs/reference/commandline/commit.md

Project version(s) affected

latest published version

Suggestions for a fix

See above

Start with docs/reference/commandline/commit.md, linked from the reported documentation page, and review the current --change syntax. Verify the Env examples and the questions about adding, deleting, and replacing variables, then update the documentation to state the supported behavior and syntax. Done means the commit reference accurately covers these cases.