Anchors hidden by fixed navbar

[ptheywood]

The sphinx theme's fixed navigation bar hides content when linking to an anchor within a page.

I.e. https://bede-documentation.readthedocs.io/en/latest/usage/index.html#requesting-resources does not always result in Requesting Resources being visible.

It does seem a little tempremental however, with the first visit to a specific anchor working in some cases, but being obscurred on a second vist.

e.g. on first visit to the page, with the link above it is visible:

but once on the page, clicking the same link in the side bar results in the heading not being visible:

I believe this is due to the javascirpt in bootstrap-sphinx.js but not 100%.