Add access descriptions for our physical offices

[CristinaRO]

When we were in 8-9 Hoxton Sq, we used to have a detailed guide to the physical layout of the space:
https://github.com/dxw/playbook/blob/a31757b24978c6d643d106da72a315b8dc713d7e/guides/office-accessibility.md

The goal of such a document is to give as much information upfront as possible considering the most frequent access needs. To minimise the friction that a D/deaf, disabled, and/or neuroatypical person encounters when deciding whether they can attend a space or not.

We know we cannot cover every single potential need, but we aim to cover as much as possible that most people wouldn't have to contact us to ask about their specific access needs. Having to ask adds to the burden that marginalised groups are already placed under, and reminds them that they are not expected in a space.

[yndajas]

Is this covered by Molly's work, at least for London?