Provide a Unique Selling Proposition for trex comparing it with Deno's new task runner

[michael-spengler]

since deno 1.20 introduced an integrated task runner (https://deno.com/blog/v1.20#new-subcommand-deno-task), it seems interesting to point out the benefits of using trex instead of deno task...

I'm not that much into the details of trex & deno task yet - so I could not directly point this out in the readme via pull request or so.

As an example use case it might be worth comparing how https://deno.land/x/snel would look like with deno task instead of using trex.