Update style guide to use f-strings (#7987)
Update style guide to use f-strings (#7987)

SKIP_FULL_CI  # Documentation-only change.

We should now use f-strings everywhere possible.

This also rewords some of the other sections to be more concise and clear.
benjyw/pants,wisechengyi/pants,wisechengyi/pants,pantsbuild/pants,pantsbuild/pants,wisechengyi/pants,jsirois/pants,benjyw/pants,wisechengyi/pants,pantsbuild/pants,wisechengyi/pants,tdyas/pants,jsirois/pants,tdyas/pants,tdyas/pants,wisechengyi/pants,tdyas/pants,jsirois/pants,tdyas/pants,wisechengyi/pants,tdyas/pants,pantsbuild/pants,wisechengyi/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,tdyas/pants,wisechengyi/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,tdyas/pants,tdyas/pants,benjyw/pants