Update raspberrypi.markdown

[outlandishlizard]

Update docs to specify that the B series works but the A series does not for Pi 3. (A series only has 512MB memory and OOMkills frequently)

Proposed change

The docs currently suggest that any RasPi 3 will work-- I just tried it on a 3A and ran into frequent OOMkills, and other portions of the home assistant docs suggest at least 1GB RAM, which the B series has but the A series does not.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

N/A

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[c0ffeeca7]

Thank you, @outlandishlizard 👍