Clarify difference between PETSc-style and argparse-style CLI options

[gthyagi]

Underworld currently uses PETSc-style command-line argument conventions, such as -uw_lc, where:

-uw_lc 0.02

This matches PETSc’s options database style (single dash followed by a descriptive name). However, the broader Python ecosystem uses standard argparse conventions where:
• long options are prefixed with double dashes (--option)
• short options use single dash with a single character (-o)
• hyphens (not underscores) separate words

For example, in argparse it would normally be:

--lc 0.02
--run-on-gadi

Request:
Please add a clear explanation in the documentation (and CLI help) that Underworld follows PETSc-style single-dash long options, and how that differs from argparse-style options. This could cover:
• Why single-dash long options like -uw_lc are used (because they tie into PETSc’s options database).
• That standard Python tools expect double dashes (--) for long options.
• How users should write scripts and examples that correctly parse Underworld options.
• A note for AI/automation tools so they generate correct CLI invocations.