Non-optional command options surrounded with square brackets in help text

`ipfs key gen`'s help text shows:

```
ipfs key gen [--type= | -t] [--size= | -s] [--]
```

However, `--type` and `--size` are required options (command errors out if they are not supplied). If these are intended to be required, it should probably look like:

```
ipfs key gen (--type= | -t) (--size= | -s) [--]
```

Start at the command definition or help-generation entry point for `ipfs key gen`, and inspect how required options are rendered in its usage text. Confirm the fix by checking that `--type` and `--size` appear outside square brackets and that the command still reports them as required.

Written by the indexing model from the issue text.