Update README

[koobs]

Now that the sysutils/iichid port has landed, update README to include at least:

• What kinds of devices might be expected to work (device classes, examples etc)
• Basic instructions for how users can check/verify if something is supported/works. Maybe something from https://larastechlab.blogspot.com/2020/01/i2c-touchpads-on-freebsd-130-current.html might be handy
• Notes on what information/feedback you want that would be helpful, and in what form

[wulf7]

Done in f019672 and 76a9a01

[koobs]

Thanks @wulf7!

If it would be handy for people to include additional system/hardware information (like pciconf, usbconfig or var/run/dmesg.boot) when reporting bugs, id would be great to include those commands in the README