Improve documentation for 'recovery_target' option

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/16/runtime-config-wal.html
Description:

Hello.
On page:
https://www.postgresql.org/docs/16/runtime-config-wal.html#GUC-RECOVERY-TARGET
It is spelled:
This parameter specifies that recovery should end as soon as a consistent
state is reached, i.e., as early as possible. When restoring from an online
backup, this means the point where taking the backup ended.

It would be nice to change `the backup` to `the base backup`, ecause now it
is not clear what kind of backup is written about.

Thank you.