Restructure README.md

These changes make the README more consistent with Compat's README.

Fix Package-Requires header

Thanks to Stefan Monnier for noticing.

Have vc-backup-diff compare adjacent versions by default

Fix thread-last indentation

This was changed with 28.1, so fixing this here will avoid unnecessary
whitespace changes in the future.

Add "Package-Requires" header

Update copyright

Change maintainer address to public inbox

Bump version to 1.1.0

Mention file size in vc-log

Add FIXME comment to vc-backup--get-real

Add Maintainer tag to package header

Mention that vc-backup is autoloaded

Fix typo in README

Print entire file name in version log

Rename vc-backup--get-read to vc-backup--get-real

Add URL header to repository

Untabify vc-backup.el

Just use a fixnum in vc-backup-diff.

Rename local variables in vc-backup-print-log

Print the user who owns the file