Add requires.io badge

[dhermes]

I activated as a test:
https://requires.io/github/GoogleCloudPlatform/gcloud-python/requirements/?branch=master

It pointed out we still have protobuf==2.6.0 for Py26, which is out-of-date. @tseaver is this still necessary?

[dhermes]

This is the badge:
https://requires.io/github/GoogleCloudPlatform/gcloud-python/requirements.svg?branch=master

[tseaver]

That pin is there from 9c8f432, whose commit message (from 2014-10-22) says:

Work around protobuf 2.6.1 install failure on Python 2.6.x.

There is a 3.0.0-alpha1 release of protobuf, which is not a good fit for us, I think (adds risky new proto3, does not explicitly call out real Py3k support, etc.)

[dhermes]

WDYT about adding the badge? At what point are badges too noisy?

---

RE: "2.6.0 vs. 2.6.1" I see, for some reason I thought the protobuf folks updated after releasing a broken version. I'm unclear why proto3 is "risky" but that isn't part of this issue, so not really worth hashing out.

[tseaver]

I just meant "risky" in the sense of "new API with unknown compatibility issues".

Ideally, we would adopt the 3.0.0 final release as our supported dependency, perhaps with notes on how to use 2.6.x (e.g., no 2.6.1 on Python 2.6), especially if they get the Python3 story sorted.

[tseaver]

Re: badge noise: I'm ambivalent. I think we are tracking our dependencies pretty thoroughly ATM, and our current pin is certainly justified (if we could find a more elegant way to spell the "avoid protobuf 2.6.1 on Python 2.6" rule, that would be OK with me).