Add home menu item

Show a Home menu item as first item on top nav.
Create an about-us page...

…that also shows up on the top menu.
Display pages on menu

This is set to True by default. Setting it explicitly just in case.
change file name...

…from join_us.md to about_us.md
Minor changes

Change slug to lower case,
Change author to multiple since this is largely based other posts.
Change Home title tuple.
Merge pull request #31 from kkingori/upstream-about

Add "About Us" page and navbar links to Home / About Us.