Update README.md

use BASE_PATH from start; fix backup size report

1. One bug was introduced recently - did not use BASE_PATH for including
subscripts (may not find subscripts if wasn't run from the main script's
dir)
2. Another bug fixed - did not report backup size if piece handle size
for more than 32 characters.

adding check_best_practices and crosscheck fix

1. adding check_best_practices
2. crosscheck fix - check only X latest days - crosscheck maybe
extremely slow with commvault and maybe other backup solutions.

archive_log_current use standby status instead

archive_log_current use standby status instead of DG variable