README updated to use redlobster.promise instead of redlobster.macro

The promise macro doesn't realize the form passed to it. 
In redlobster.macro:
```clojure
(defmacro promise
  "Return a promise that will be realised by the given forms. The functions
`realise` and `realise-error` will be available inside the macro body, and one
of these should be called at some point within the forms to realise the promise."
  [& forms]
  `(let [promise# (redlobster.promise/promise)
         realise# (fn [promise# value#]
                    (redlobster.promise/realise promise# value#))
         realise-error# (fn [promise# value#]
                          (redlobster.promise/realise-error promise# value#))
         ~'realise (partial realise# promise#)
         ~'realise-error (partial realise-error# promise#)]
;; forms is never passed to redlobster.promise to realise
     ~@forms
     promise#))
```
This is why I believe I get a timeout when I use this macro as a handler:
```clojure
(defn handler [request]
      (promise {...}))
(run-http-server handler )
```