Add note about raspi cam options being ignored

[pdfowler]

Myself, and others have run into the problem of setting options for camera_raspi_options only to have them be ignored. It appears that this is due to some pi cam modules being detected as USB cams and not pi cams as described in #674

Short of rewriting the camera detection code, this PR adds a note in the base octopi.txt to help people running into the issue.

The note reads:

NOTE: Newer raspi cam modules are reporting as usb devices causing these options to be ignored. Set `camera="raspi"` to avoid these 

[guysoft]

@foosel can you confirm before I possibly confuse a lot people?

[pdfowler]

Re-reading it, I think including a link to #674 would be useful. Maybe:

NOTE: Newer raspi cam modules are reporting as usb devices causing these options
to be ignored. See https://github.com/guysoft/OctoPi/issues/674 for more information. 
Set `camera="raspi"` to avoid these issues.

[foosel]

Don't have the hardware to confirm in person but can confirm that we saw that on the forums and it's caused some confusion that this would help mitigate.

Better would be new detection code but I can't help there at the moment, no hardware and no time.

[guysoft]

No hardware here neither to test, merging.