Specify Python 2 and IPython 5.x LTS in README.md (#1003)
Specify Python 2 and IPython 5.x LTS in README.md (#1003)

* Specify Python 2 and IPython 5.x LTS in README.md

Angr is not yet compatible with Python 3 or [IPython 6 or 7](https://github.com/ipython/ipython).

* Clarify supported IPython versions

iamahuman/angr,angr/angr,tyb0807/angr,schieb/angr,schieb/angr,tyb0807/angr,angr/angr,angr/angr,iamahuman/angr,schieb/angr,tyb0807/angr,iamahuman/angr