Add MS Word guidance to Self-assessment Exercise Downloads

[nickaddy]

Background
In order to minimise user-generated issues with the new SA upload extraction process, we would like to share guidance with SETs so they can lock down their Word document before adding to the Downloads section

Feature(s)

• Add link to Word guidance on modal that appears when users click on Add to upload their SA template

• Link to this file to open in a new window/download How to restrict access to selected sections of Word documents.pdf

[nickaddy]

Hey team! Please add your planning poker estimate with Zenhub @drieJAC @HalcyonJAC @tomlovesgithub @warrensearle

[warrensearle]

The PDF may need to be stored in firebase storage.