Enable tab completion of commands/workspace names

The `click` framework provides tab completion for more or less free, however
it does need to be enabled. This PR adds the requirements to set up tab
completion to the README.md, as well as adds completion support for
Workspace names to the `boardwalk workspace use` command. Prior to this,
knowing the full workspace name would be required, thus requiring the user
to look in the Boardwalkfile, or run `boardwalk workspace list` beforehand.

Resolves internal ticket SVRENG-493.

README.md

@@ -169,6 +169,34 @@ release, minus 1 minor version. So, if the current stable version is `3.22.x`,
 Boardwalk should work with `3.21.x`. Consider using
 [`pyenv`](https://github.com/pyenv/pyenv) to maintain fresh python environment.
 
+#### Shell Completion
+
+To enable shell completion for `boardwalk` and `boardwalkd`, the following set
+of commands will generate the completion script and add them to your shell (a
+shell restart will be needed):
+
+##### Bash
+```bash
+_BOARDWALK_COMPLETE=bash_source boardwalk > ~/.boardwalk-complete.bash
+_BOARDWALKD_COMPLETE=bash_source boardwalkd > ~/.boardwalkd-complete.bash
+echo '. ~/.boardwalk-complete.bash' >> ~/.bashrc
+echo '. ~/.boardwalkd-complete.bash' >> ~/.bashrc
+```
+
+##### Zsh
+```zsh
+_BOARDWALK_COMPLETE=zsh_source boardwalk > ~/.boardwalk-complete.zsh
+_BOARDWALKD_COMPLETE=zsh_source boardwalkd > ~/.boardwalkd-complete.zsh
+echo '. ~/.boardwalk-complete.zsh' >> ~/.zshrc
+echo '. ~/.boardwalkd-complete.zsh' >> ~/.zshrc
+```
+
+##### Fish
+```sh
+_BOARDWALK_COMPLETE=fish_source boardwalk > ~/.config/fish/completions/boardwalk.fish
+_BOARDWALKD_COMPLETE=fish_source boardwalkd > ~/.config/fish/completions/boardwalkd.fish
+```
+
 #### Container Install
 
 Boardwalk may be built as a container image by running `make container`.