add thumbnail to README
add thumbnail to README

pgranieri/pgranieri.github.io,KaiJin11/KaiJin11.github.io,gisdjango/gisdjango.github.io,KaiJin11/KaiJin11.github.io,KaiJin11/KaiJin11.github.io,pages-themes/midnight,gisdjango/gisdjango.github.io,pgranieri/pgranieri.github.io,pgranieri/pgranieri.github.io,gisdjango/gisdjango.github.io,pages-themes/midnight,gisdjango/gisdjango.github.io,KaiJin11/KaiJin11.github.io,pages-themes/midnight,pages-themes/midnight,pgranieri/pgranieri.github.io