Add releases folder with Terra 0.6 and 0.7 release guides. (#447)

* Add release folder with Terra 0.6 and 0.7 notebooks

* Remove apple junk

* Make things look better in github

* Clear massive text circuit that doesn't look nice on github

* Removed references to mapper, added more info about backends and pip install

* Move releases dir out of qiskit dir

* Add a transition line

* Remove mention of Aqua

Author: dongreenberg