3id-did-resolver README.md should be update

Hi, usage code in the 3id-did-resolver's README.md doesn't match the actual code.

If I use usage code in README as below :
``` typescript
import ThreeIdResolver from '@ceramicnetwork/3id-did-resolver'
import { Resolver } from 'did-resolver'

// You need an instance of Ceramic to call getResolver.
// This can be either @ceramicnetwork/core or @ceramicnetwork/http-client.
// You can also set an address for your own ethr-did-registry contract
const ceramic = // ...

// getResolver will return an object with a key/value pair of { '3': resolver }
// where resolver is a function used by the generic did resolver.
const threeIdResolver = ThreeIdResolver.getResolver(ceramic)
const didResolver = Resolver(threeIdResolver)

const doc = await didResolver.resolve('did:ethr:0xf3beac30c498d9e26865f34fcaa57dbb935b0d74')
console.log(doc)
````
It will comes the error like :

Usage code in README should be modified to :
``` typescript
import { getResolver } from '@ceramicnetwork/3id-did-resolver'
import { Resolver } from 'did-resolver'

// You need an instance of Ceramic to call getResolver.
// This can be either @ceramicnetwork/core or @ceramicnetwork/http-client.
// You can also set an address for your own ethr-did-registry contract
const ceramic = // ...

// getResolver will return an object with a key/value pair of { '3': resolver }
// where resolver is a function used by the generic did resolver.
const threeIdResolver = getResolver(ceramic)
const didResolver = new Resolver(threeIdResolver)

const doc = await didResolver.resolve('did:ethr:0xf3beac30c498d9e26865f34fcaa57dbb935b0d74')
console.log(doc)
```

Start with the 3id-did-resolver README.md usage example and compare its imports and Resolver construction with the package's current API. Update the example so it matches the working usage shown in the issue; it is done when the documented snippet is consistent with the actual exports and can be followed without the reported error.

Written by the indexing model from the issue text.