Small tweaks home page

[aloctavodia]

A large redesign is being discussed in #113, which is a huge improvment, in the meantime, this PR introduces small changes to the current page. Some problems are:

• Announcements are outdated
• Citation information is missing
• The "Get started" section comes after a long example (for a home page).
• The pymc-labs logo is missing. This gives a 404 https://github.com/pymc-labs/brand/blob/main/logos/4-pymc-labs-transp-black.png?raw=true @twiecki do you know the correct location of the logo file?