Expanded the Options section, added caveat in Production-Ready section

[danburzo]

I propose two changes to README.md:

1. Better documentation of user-configurable options, which are not apparent (as far as I could tell) unless reading through the source code.
2. A caveat in the production-ready section, since it was a bit surprising that after a (long-due) update in our Scribe instance, it stopped working in Safari 8 and Chrome 45 (due to missing support for Object.assign -- which BTW is easily patched with a polyfill, something worth considering?)

[rrees]

I can see why you want the expanded documentation but I might add them into the wiki or a docs folder rather than README since they are not things you need to access frequently. I will also add a version note to things like the default plugin list which will change in future. Hope that's okay with you.

Version 3 of Scribe was a deliberately breaking change (hence a major version number) but you're right that it would be sensible to add some notes about what people might need to polyfill for older browsers.

Thanks for contributing!

[danburzo]

Sounds good! 👍