bug: chalk docker autocomplete

[numerical]

Adds the _chalk_docker_autocompletions function to autocomplete docker commands

• Followed the steps in the contributor's guide: https://crashoverride.com/docs/other/contributing#filing-the-pull-request
• PR title uses semantic commit messages
• Filled out the template to a useful degree
• Updated CHANGELOG.md if necessary

Issue

#281

Description

Small one line change to add autocompletions for docker commands

Testing

source autocompletion file, and run chalk docker <tab><tab> and chalk docker rmi <tab><tab> to confirm whether tab completion is working for docker and docker subcommands