Add required changes to installation instructions (#242)

* Add required changes to installation instructions

* In 3.6 days, the env install needs to specify that it needs to be a 3.5 env
* plio is not available in the given channels, so I added an install command that pulls it from the USGS channel

* Add code encapsulation

* Fix RST markup

* Really fix the darn markup

* Adapted the install instructions again

According to Jay, he's not using the jlaura channel anymore.
Added comment about fixing either python 3.5 or 3.6, but left it free in the given install command line.