Add disclaimer about non-working examples in readme

[milesfrain]

Related to #61

[milesfrain]

We could alternatively update the examples so they compile, but that becomes noisy and shifts focus towards how to use the other libraries. For example, this is what's required to get the first example working.

import Affjax as Ajax
import Affjax.ResponseFormat as ResponseFormat
import Data.Either (Either(..))
import Effect (Effect)
import Effect.Aff (Fiber, launchAff)
import Effect.Class.Console (log)

main :: Effect (Fiber Unit)
main = launchAff do
  result <- Ajax.get ResponseFormat.string "http://example.com"
  case result of
    Left err -> log $ "GET failure: " <> Ajax.printError err
    Right response -> log $ "GET response: " <> response.body

Another option is to just show examples involving delay (as is done in the tests).

import Effect (Effect)
import Effect.Aff (Fiber, Milliseconds(..), delay, launchAff)
import Effect.Class.Console (log)

main :: Effect (Fiber Unit)
main = launchAff do
  log "hello"
  delay $ Milliseconds 1000.0
  log "world