Make note of common yum.conf (mis)configurations

Ran into this today when installing this.  Couldn't install the PECL package, as the default Yum.conf file excluded php* packages.
Typo / spacing fix.

https://www.youtube.com/watch?v=tcGQpjCztgA
Merge pull request #43 from JustinSainton/patch-1

Make note of common yum.conf (mis)configurations.