Update README and docs index pages

[brainwane]

Add register documentation to README and add basic information to docs index.

Fixes #46.

(Incidentally, I tried to run tox -e pep8, but got: twine/utils.py:39:18: F821 undefined name 'raw_input' which I don't know how to address.)

[codecov]

Codecov Report

Merging #292 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #292   +/-   ##
=======================================
  Coverage   67.42%   67.42%           
=======================================
  Files          12       12           
  Lines         574      574           
  Branches       91       91           
=======================================
  Hits          387      387           
+ Misses        162      161    -1     
- Partials       25       26    +1

Impacted Files	Coverage Δ
twine/wininst.py	29.72% <0%> (ø)	⬆️

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[erikrose]

The raw_input thing probably happens under Python 3, where all input() is raw.

[sigmavirus24]

Register needs to be deprecated and is presently broken (as pypi.org disabled that API). I'm wondering if we should document this anyway or if we should omit it.

[brainwane]

My inclination is to document it (and to mention that it is broken and about to be deprecated) until we actually deprecate it, and then to remove the documentation.

[brainwane]

I reviewed #200, pypi/warehouse#1627 and other related issues and added pointers about the register command to the README.

[sigmavirus24]

✨ Thanks @brainwane! ✨