Programmer's Guide: Add a description of optimization levels in the $OPTIMIZATION directive

https://www.freepascal.org/daily/doc/prog/progsu60.html

The documentation for LEVEL1..LEVEL4 doesn't specify what these levels actually do:

LEVEL1
Enable some level 1 optimizations. Note that this is not the same as -O1, it is a separate flag.
LEVEL2
Enable some level 2 optimizations. Note that this is not the same as -O2, it is a separate flag.
LEVEL3
Level 3 optimizations. Note that this is not the same as -O2, it is a separate flag.
LEVEL4
Level 4 optimizations. Note that this is not the same as -O2, it is a separate flag.