Expand "Members" menu

We would like to make the "Members" menu into a drop-down menu with the top level changing to "Membership"

Membership

• Our Member
• Become a Member (move everything from https://sdv.eclipse.org/about/ that is below the "WHY SHOULD YOU JOIN?" heading)

@paulinagueorguieva @sgallian @dana please let me know if you have any concerns with this recommendation.