Add accessibility page

[FromAnkyra]

It would be nice to have a regular page that discussed the various accessibility related things we do, as well as how to contact us if you have access needs that aren't being met. The page would list things such as:

• We use the computer science building for most our events, and we make sure that events outside that take place in wheelchair accessible venues (checking for lift access especially)
• We tend to have a “quiet area” for most of our social events, especially when they get rather loud
• For our virtual social events, we attempt to have structure to them to make them less stressful for everyone involved
• Our talks are not sign language interpreted, however, we caption every talk we put onto our youtube channel
• When we have homemade foods at our event, we list all allergens
• we hold coffeescript at a venue where many food necessities are catered for

[LukeMoll]

Probably a consideration when adding a (new) page, the navbar is getting pretty crowded, the social links could probably do with being collapsed into a single "contact us" submenu or page.

[LukeMoll]

Also more relevantly, seems ideal to put a call to action "any questions suggestions, email us or talk in chat"

[FromAnkyra]

note: we cannot afford to provide interpretors by default, but should add a line saying that we'll contact uni a11y if needed to provide one