Add why-is-youtube-so-successful.md post skeleton

Add 2014-11-08-why-is-youtube-so-successful.md post skeleton.
Update welcome post category
Add why-is-youtube-so-successful.md

Add 2014-11-08-why-is-youtube-so-successful.md. This commit relates to
issue #7.
Minor grammar and spelling changes

Alter and fix minor grammar and spelling issues in 2014-11-08-why-is-youtube-so-successful.md.
Add link to CrashCourse YouTube Channel
Merge pull request #8 from psgs/youtube

Add why-is-youtube-so-successful.md
Merge pull request #9 from psgs/master

Add YouTube post, update welcome post category