Add help for challenging color card detection

[HaleySchuhl]

Is your feature request related to a problem? Please describe.
Color card detection is sensitive to picking up other square shapes in an image, such as calculator buttons and tape grids and additional color cards.

Describe the solution you'd like

• Add recommendations to the FAQ page of the plantcv docs
• Add optional ROI/mask for excluding parts of the image in the detection algorithm pcv.transform.detect_color_card and implement into pcv.transform.auto_correct_color

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context, sample data, or code relevant to the feature request here.