Add a tutorial explaining the generally accepted input types

[seisman]

Inspired by PR #1186.

For GMT CLI, there are mainly two types of input: a table or a grid. PyGMT is more powerful and can accept more input types.

For a table input, PyGMT functions generally accept the following input types:

• a file name to a ASCII table, e.g., data="input.dat"
• a 2d numpy array, pandas.DataFrame, e.g., data=data
• a single value of int or float or str type to x,y, e.g., x=5.0, y=5.0
• a list to x and y, e.g., x=[1.0, 2.0], y=[3.0, 4.0]
• a 1d numpy array to x and y, e.g., x=np.array([1.0, 2.0]), y=np.array([3.0, 4.0])
• a geopandas.GeoDataFrame (see Integration with geopandas to plot shapely geometries #608 & Handle geopandas and shapely geometries via geo_interface link #1000)
• an xarray.Dataset
• io.StringIO (once RFC Allow for io.StringIO inputs to certain modules #576 is done)
• more?

For a grid input, PyGMT functions generally accept the following input types:

• a file name to a grid file, e.g., grid="input_grid.nc"
• xarray.DataArray, e.g., grid=grid
• more?

Although these various input data types are already used in different tutorials and examples, I think it would be better to have a standalone tutorial, explaining these input types.

[weiji14]

Also should mention that plotting shapefiles directly using plot and plot3d (maybe others too?) is supported. Xref #1616 and https://docs.generic-mapping-tools.org/6.3/cookbook/file-formats.html?highlight=shapefile#shapefiles

[seisman]

pathlib.Path support was added in #1382.