Resolve "Add ICAT field table with units and description to docs"

Closes #38 (closed)

In this MR I document the ICAT fields by dividing them in scrollable tables.

I have no HTML/CSS experience so feel free to suggest a better way.

I was trying to show the tables in horizontal tabs by playing with the CSS parameters but I failed

.tabs {
    display: flex;
    flex-direction: row;
}