This is useful for annotating completion-read buffer results which all
belong to a single project, as it removes the project root from the
file path field, showing a relative path to each buffer's file from the
project root.
The default 'marginalia-annotate-command annotation method for M-x
candidates has a small but perceivable performance impact as you
type. The 'marginalia-annotate-binding method does not have any
perceivable performance impact.
Also I only really care about seeing keybindings in the M-x list, I can
definitely live without command descriptions.