Add paragraph and example for using wildcart for `--allow-net`

[csvn]

The docs did not show that it's possible to use * as wildcard for subdomains when using hostname for --allow-net.

deno run --allow-net="*.auth0.com" main.ts

Just using "auth0.com" will not allow ".eu.auth0.com". To allow any subdomain with --allow-net, a wildcard must be used. This proposed change should hopefully make the docs clearer on how to correctly configure permissions.

This is extra important now that it's possible to configure permissions via deno.jsonc, which makes it easier to make more details settings for permissions:

{
  "permissions": {
    "default": {
      "net": ["*.auth0.com"]
    }
  }
}