Add a gallery example to show coloring of points by categories (#1006)
Add a gallery example to show coloring of points by categories (#1006)

Provide gallery example to show coloring of points by categories.
Uses the Palmer Penguins example dataset loaded into a pandas
DataFrame, with the categorical dtype column converted to int type.

Co-authored-by: Wei Ji <9490087a8b98c7de12813b2e194ef86ac3043a88@users.noreply.github.com>
Co-authored-by: Dongdong Tian <3eae6d0b95aef6af8a0d785fe9f127268703c43c@gmail.com>
Co-authored-by: Yao Jiayuan <4a3b81659a3e41c1b1e422525b254e800e0ba11d@gmail.com>

GenericMappingTools/gmt-python,GenericMappingTools/gmt-python