doc(cli/flags): Reduce empty lines in help messages, rewrite a bit

[nayeemrmn]

It's annoying to scroll through in short integrated terminals. Also remove copy of the help text from the manual (which was outdated).

deno 0.35.0
A secure JavaScript and TypeScript runtime

Docs: https://deno.land/std/manual.md
Modules: https://deno.land/x/
Bugs: https://github.com/denoland/deno/issues

To run the REPL supply no arguments:

  deno

To evaluate code from the command line:

  deno eval "console.log(30933 + 404)"

To execute a script:

  deno https://deno.land/std/examples/welcome.ts

The default subcommand is 'run'. The above is equivalent to

  deno run https://deno.land/std/examples/welcome.ts

See 'deno help run' for run specific flags.
...

->

deno 0.35.0
A secure JavaScript and TypeScript runtime

Docs: https://deno.land/std/manual.md
Modules: https://deno.land/std/ https://deno.land/x/
Bugs: https://github.com/denoland/deno/issues

To start the REPL, supply no arguments:
  deno

To execute a script:
  deno run https://deno.land/std/examples/welcome.ts
  deno https://deno.land/std/examples/welcome.ts

To evaluate code in the shell:
  deno eval "console.log(30933 + 404)"

Run 'deno help run' for 'run'-specific flags.
...

etc.

[ry]

LGTM - thanks