Added banner-772x250.png and screenshot-1.png

git-svn-id: https://plugins.svn.wordpress.org/simple-price-calculator-basic/trunk@990366 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme.txt to include name of plugin

git-svn-id: https://plugins.svn.wordpress.org/simple-price-calculator-basic/trunk@990367 b8457f37-d9ea-0310-8a92-e5e31aec5664