This commit adds a new widget, "Update", which will check for komorebi
version updates using the cargo package version of the running binary
and the latest release returned from the GitHub API.
If the latest release is newer than the current cargo package version, a
widget will be shown, which can be clicked to open the changelog of the
latest release.
This commit adds instructions for komorebi-bar to the Getting Started
section of the documentation website, adds an example komorebi.bar.json
configuration file, integrates that file with the quickstart command,
and updates the start and stop commands to take --bar flags similar to
the --whkd flags.
In updating the documentation I also decided to rename in the internal
tag for the KomobarTheme and KomorebiTheme enums to "palette" instead of
the previous generic "type" tag which was copied from the serde docs.
