Add the changes in send to the migration guide

### Description

I just noticed that we haven’t documented all the changes made in send; we’ve only documented the change that send.mime no longer exists, but there were other changes that directly affect Express.

https://github.com/pillarjs/send/blob/master/HISTORY.md#100-beta1--2022-02-04

Discovered in https://github.com/expressjs/express/issues/6450

### Expectations

We need to document it