This was originally added in meichthys#35 but lost in e81d717 accidentally.

This style sheet does a few things

* Changes the table height to 75% of the size of the viewport so you can see more rows
* Sticky the header row and the left-most column so you can always see the photo library name and the attribute name while you scroll horizontally or vertically

This solves a few problems with the current table as viewed through GitHub's repo rendering of the `readme.md`

* The horizontal scrollbar is only at the bottom of the table so you have to scroll to the bottom to scroll right and left at which point you can't see the table header showing the name of the photo library
* When you scroll down the photo library name doesn't stay at the top of the table, it dissapears

This fixes a typo in the JSON config of markdown-link-check
and a missing language for a code block in the readme

The pigallery2.onrender.com demo URL changed, this accommodates that.
The SnapCrescent Demo site is serving up 503s (reported in snapcrescent/snapcrescent#52 ) so this disables link checking on it.