[Minor] Ignore or complain about custom commands which don't have required annotations

[rfay]

Describe the bug

Apparently in v1.16+, custom/script commands that don't have a "Usage" annotation don't get properly shown in the list of commands (they're without a command name).

To Reproduce

Use this command as .ddev/comamnds/web/badcmd:

#!/bin/bash
## Description: This command won't show up properly

tr -cd '[:alnum:]' < /dev/urandom | fold -w32 | head -n1

If you type ddev you'll see it doesn't get labelled correctly:

Create and maintain a local web development environment.
Docs: https://ddev.readthedocs.io
Support: https://ddev.readthedocs.io/en/stable/#support

Usage:
  ddev [command]

Available Commands:
                   This command won't show up properly (shell web container command)
  auth             A collection of authentication commands

Expected behavior

In v1.15.3 a command like this would work, with the name of the script as the name.

IMO it's fine for commands to require the Usage annotation, but if they don't have it ddev should complain I think.

Note that this command works fine in .ddev/commands/web/ttpwd:

#!/bin/bash
## Description: Generate 32 character alphanumeric password
## Usage: ttpwd

tr -cd '[:alnum:]' < /dev/urandom | fold -w32 | head -n1