Updated section on What's In The Sources?

Signed-off-by: Conrad Gomes <conrad.s.j.gomes@gmail.com>
Added the following sections 'Browsing The Sources', 'Getting Accustomed To Browsing The Sources'. Added content to the first objective of 'Getting Accustomed To Browsing The Sources'.

Signed-off-by: Conrad Gomes <conrad.s.j.gomes@gmail.com>