index: Add 2020 infographic from @smeragoel (closes #154)
    
    This commit adds the 2020 infographic created by @smeragoel into our
    docs repository. It also adds it to the home page for the D&I docs. I
    figure a visual says a lot more than pictures, so I placed it near the
    top of the document.
    
    I also added a table of contents (`:toc:`) to help make the content on
    the lower part of the page more known and not buried by the infographic.
    
    Closes #154.
    
    Signed-off-by: Justin W. Flory (he/him) <git@jwf.io>