Added Social Media Buttons, Fixed "Welcome!" Color

Added bootstrap social media buttons and created “main.css” file in
Documents>Georgiafs.github.io to link to “index.html” through
bootstrap. Corrected “Welcome!” color problem (didn’t need space
between “rgba” and “(…)”
Changed “h2” from “Unforgettable Books” to “Mrs Knicker’s best books”
Change header img border from “beige” to “solid black”