Update documentation to better explain the impact of changing the synced folder name

[scottslowe]

When the synced-folder component is used to create a synced folder, a resource name is supplied, as in this TypeScript example:

const folder = new synced.S3BucketFolder("synced-folder", {
        path: "./testdata",
        bucketName: "somebucketname",
        acl: aws.s3.BucketOwnerFullControlAcl,
        managedObjects: false
    });

If this resource name is changed (say, from synced-folder to synced-s3-folder), this results in the creation of an entirely new resource. As a result, Pulumi will remove the old resource. This behavior is by design, but perhaps may be unexpected to some users. To help address this, we should update the documentation for this component to properly explain this behavior.

This update should include changes to both the documentation in this repository as well as the Pulumi Registry.