Make --help output more detailed.

[sebastiancarlos]

Hello,

For my personal use, I updated the --help output to clarify a bit the behavior (particularly highlighting the importance of putting everything compiler-related in the first argument, and the need for a final -- in that argument when used as a shebang.

Current --help:

Usage: c <file.c ... | compiler_options ...> [program_arguments]
       c --clear-cache
Execute C programs from the command line.

  Ex: c main.c
  Ex: c main.c arg1 arg2
  Ex: c 'main.c other.c' arg1 arg2
  Ex: c 'main.c -lncurses' arg1 arg2

This PR's --help:

Usage:
       c '<file.c ... | compiler_options ...>' [program_arguments]
       c --clear-cache

Usage for shebang with extra compiler options:
       c '<other.c ... | compiler_options ...> --' <file.c> [program_arguments]

Execute C programs from the command line.

  Ex: c main.c
  Ex: c main.c arg1 arg2
  Ex: c 'main.c other.c' arg1 arg2
  Ex: c 'main.c -lncurses' arg1 arg2

Execute C programs when "main.c" is executable with shebang.

  Shebang: #!/usr/bin/env c
  Shebang: #!/usr/bin/env -S c 'other.c --'
  Shebang: #!/usr/bin/env -S c '-lncurses --'
  Ex:      ./main.c
  Ex:      ./main.c arg1 arg2

Feel free to merge if you like it. Cheers!