Address questions regarding suitability for storage and untrusted inputs (#346)
Address questions regarding suitability for storage and untrusted inputs (#346)

* Address questions regarding suitability for storage and untrusted inputs

Puts some prominent text into the `readme.md` regarding some use cases
that are likely to be common, along with a few hopefully helpful
pointers to avoid footguns.

Closes #345, closes #216, addresses #240, #266.

* Fix typos in `readme.md`

* Remove confusing sentence post 1.0, as requested
servo/bincode,TyOverby/bincode