Add explainer panels

[jshook]

It would be nice to be able to associate some text or markdown with a plot where we could put explainer text about what the plot entails. This could be a hover effect or any other form of "openable' text box.

Some text blurbs that might support this are as follows:

for random read tests

This random read test measures the throughput and latency of operations at ___ byte read sizes directly from the storage device without buffering. It is used to establish the throughput and the latency characteristics of the device under throughput or operational saturation at this read size, uncontended with other operations.

for mixed workload tests:

This mixed workload test measures the throughput and latency of random reads between 1k and 4k read sizes, uniformly distributed, directly from the storage device without buffering, while concurrently streaming reads and writes at up to 10 MB/s each. This is used to establish the variation in reads with respect to uncontended operations in the random read tests. It also establishes a reference point for interpreting where streaming reads and writes start to saturate the device or IO channel, which significantly impacts random read latency.

.. and so forth.