How to add labels

Was looking for this to pass on to a new product owner and couldn't find it so quickly dropped her this note:

To add labels you click on the little cog next to the word labels (right hand sidebar on an issue) and scroll down until you find the priority ones - then just click on the relevant one and click back on the little cog.

An explanation of what each of these means can be found here: https://github.com/dwyl/labels#labels

To be reworded and added to readme.