[Webcom] Logo page updates

[Jason Birch]

Hi all,
 
I've made some updates to the logos page, linking to the branding guide, and adding a bit of information about the origin of the logo.  Feel free to correct any mistakes / oversights.  We should contact Aaron about setting up a page for him; it was part of the contest benefits.  Also wondering if he ever got his swag...
 
https://www.osgeo.org/logos
 
I'm also going to add this to the left-side Foundation content block.
 
Jason