Add more detail for sub-commands' help messages

[Gedochao]

Context: #1669

This is the first batch of help tweaks aiming at improving their usefulness.
It focuses on individual sub-commands' help messages (and not their options' help messages, which will be addressed separately).

Example for the run sub-command:

▶ scala-cli run --help
Usage: scala-cli run [options]
Compile and run Scala code.

Specific run configurations can be specified with both command line options and using directives defined in sources.
Command line options always take priority over using directives when a clash occurs, allowing to override configurations defined in sources.
Using directives can be defined in all supported input source file types.

For a run to be successful, a main method must be present on the classpath.
.sc scripts are an exception, as a main class is provided in their wrapper.

Multiple inputs can be passed at once.
Paths to directories, URLs and supported file types are accepted as inputs.
Accepted file extensions: .scala, .sc, .java, .jar, .md, .jar, .c, .h, .zip
For piped inputs use the corresponding alias: _.scala, _.java, _.sc, _.md
All supported types of inputs can be mixed with each other.

To pass arguments to the actual application, just add them after `--`, like:

```sh
/Users/pchabelski/IdeaProjects/scala-cli/out/cli/base-image/nativeImage.dest/scala-cli run Main.scala AnotherSource.scala -- first-arg second-arg
```

For detailed documentation refer to our website: https://scala-cli.virtuslab.org/docs/commands/run

Help options:
  --usage                                        Print usage and exit
  (...)