With MDL-81031 psr/log was added to moodle core, so amending the instructions
in readme_moodle.txt accordingly.
Notable upstream changes:
- With the upstream PR #422 the file `source/CAS.php` is now also
autoloaded.
- With the upstream PR #428 the list of composer ignored files got
updated. So we can now remove some of the upgrade steps in the
readme_moodle.txt
Signed-off-by: Daniel Ziegenberg <daniel@ziegenberg.at>