Document --heap-size-hint in Command-line Interface (#50480)

Almost a direct copy of the output in `julia --help`.


Closes #50588

Co-authored-by: Max Horn <max@quendi.de>

doc/src/manual/command-line-interface.md

@@ -213,6 +213,7 @@ The following is a complete list of command-line switches available when launchi
 |`--output-incremental={yes\|no*}`      |Generate an incremental output file (rather than complete)|
 |`--trace-compile={stderr,name}`        |Print precompile statements for methods compiled during execution or save to a path|
 |`--image-codegen`                      |Force generate code in imaging mode|
+|`--heap-size-hint=<size>`              |Forces garbage collection if memory usage is higher than that value. The memory hint might be specified in megabytes (e.g., 500M) or gigabytes (e.g., 1G)|
 
 
 !!! compat "Julia 1.1"