Add TIFF examples

[ziw-liu]

          It would also be very helpful to include examples of the new slicing and string-indexing that xarray enables. Most/all of the official `iohub` examples currently focus on the zarr reader/writer.

Originally posted by @ieivanov in #185 (review)

[ziw-liu]

All of the example scripts are about NGFF or CC. That's because these are the formats we can write with iohub so test data doesn't need to be downloaded during documentation building. We can ask developers to always run pytest before building docs so the test data can be reused. But this will likely be a fragile hack.

#185 (comment)