Update README.md

[saalmaan]

pip tamper should be install with admin rights because some other dependencies during installation though error, and already some users have reported similar issues.

[dutzi]

I guess it is a pretty common issue, but the right way to go with this is using virtualenvs.
On one hand, it's not so popular/known. On the other hand, most pip packages on Github state you should do "pip install ", not "sudo pip install...". So I get the feeling we will be doing something wrong by having the docs suggest you should use sudo...