SPI RGB LED component description

[clydebarrow]

Description:

Add documentation for the spi_rgb_led component.

Related issue (if applicable): fixes

Pull request in esphome with YAML changes (if applicable): esphome/esphome#5288

Checklist:

• I am merging into next because this is new documentation that has a matching pull-request in esphome as linked above.
  or

• I am merging into current because this is a fix, change and/or adjustment in the current documentation and is not for a new component or feature.

• Link added in /index.rst when creating new documents for new components or cookbook.

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[kbx81]

Oh! We need to add this to the index, as well. 😄

[clydebarrow]

Oh! We need to add this to the index, as well. 😄

There's an index? Or do you mean the TOC - https://esphome.io/#light-components

[kbx81]

Oh! We need to add this to the index, as well. 😄

There's an index? Or do you mean the TOC - https://esphome.io/#light-components

Yup, that's the right place -- I believe it's index.rst.