Add filters to links list

[matmaxgeds]

e.g. following: https://matmaxgeds.github.io/filtered-links-page/index.html

Also need to figure out how to allow two buttons to be pressed at the same time i.e. tools for (AND) publishers

Publishers - Users
Tool - Guidance
Technical - Non technical - this one needs adding
Grateful for more input on these

[matmaxgeds]

I added a PR here: #15 - but also need to:

• update the Readme to indicate how to add the classes to the links
• it works on Firefox - but I think goes into two lines on chrome - so widen the container or see why font size extra css is not working the same - or swap 'both' for 'and'....
• change button spelling of 'non technical to 'non-technical