README.md logo missing

[cpswan]

Describe the bug

https://atsign.dev/assets/img/atPlatform_logo_gray.svg disappeared during the recent migration to a Gitbook generated site

To Reproduce
Steps to reproduce the behavior:

1. Browse to https://github.com/atsign-foundation/docs
2. See the missing logo

Expected behavior
Logo is shown (preferably in colours that match dark/light themes)

Screenshots

[XavierChanth]

I think I'll have to make a manual list this time round... git-xargs did not pick up every repo clearly.

[cpswan]

This is also impacting the atsign-company READMEs etc.

NB I've noticed we seem to be missing a </h1> closing tag on the logos line(s). It doesn't seem to be causing problems.

I've raised atsign-company/.github#4 right away to fix the org profile