fix: docs shouldn't require ready cores (#29)

We no longer require cores to be ready as of
89ac7ae ([pull request #24][0]). This
updates the docs to reflect that.

[0]: #24

README.md

@@ -58,8 +58,6 @@ const cores = [
   new Hypercore('./core2'),
 ]
 
-await Promise.all(cores.map(c => c.ready()))
-
 const indexer = new MultiCoreIndex(cores, { storage: createStorage, batch })
 
 ```
@@ -75,7 +73,7 @@ Type: `Array<Hypercore>`
 
 An array of [Hypercores](https://github.com/hypercore-protocol/hypercore-next)
 to index. All Hypercores must share the same value encoding (`binary`, `utf-8`
-or `json`). All Hypercores must have a `key` property that is populated, either by waiting for all of them to be ready or by instantiating them with the `key` opt.
+or `json`).
 
 ### opts