docs(changelog): update storage documentation

[renansigolo]

Checklist

• Issue number for this PR: Error in documentation for Uploading blobs #1616, Example doesn't work with newest version: AngularFireUploadTask.downloadURL(); returns undefined #1645 (required)
• Docs included?: yes (yes/no; required for all API/functional changes)
• Test units included?: yes (yes/no; required)
• In a clean directory, yarn install, yarn test run successfully? yes (yes/no; required)

Description

Updating the documentation with examples on how to upload files through the methods, put, putString and upload.

Code sample

[jamesdaniels]

Not on task any longer; might want to point out it's on the ref.

[renansigolo]

I'd updated the example with a more thorough description of this change, moreover, I've noticed that the type of the Observable changed to getDownloadURL(): Observable<any>, instead of getDownloadURL(): Observable<string>, thus I've matched the new declaration at the docs. storage ref - line 7

[jamesdaniels]

You'll need to wait for task to finish, see Jeff's comment for a good solution #1649 (comment)

[renansigolo]

Even though I've added Jeff's example, on my tests I was only able to retrieve the url by actually subscribing to the Observable that receives the data from the getDownloadURL() function inside the finalize method.

There's an example

import { finalize } from 'rxjs/operators';

// ...

task
   .snapshotChanges()
     .pipe(
        finalize(() => {
           this.downloadURL = storageRef.getDownloadURL()
           this.downloadURL.subscribe(ref => {
           this.update(this.user, ref)
           })
        })
     )
.subscribe()

[rafaelzuckerberg]

Thanks

[jamesdaniels]

Thanks for taking a pass on this, just a couple small things.