Improve docs on post find hooks

[tom-thorne]

Using mongoose 5.18.11
Do you want to request a feature or report a bug?
Documentation Bug

The callback type on schema hook for post 'find' is unclear. I had assumed it was an array, but now after commit
4dad667 it is also a doc.

// what type is arg - is it an array or a doc ?
Schema.post('find', (arg: any) => {
  ...
});

It would be super helpful if the documentation made it clearer what the types used in hooks should be.

[vkarpov15]

@tom-thorne arg should always be an array. We'll see if we can repro the case where it is a doc.

[IslandRhythms]

const mongoose = require('mongoose');

const run = async () => {
    await mongoose.connect('mongodb://localhost:27017/test', {
      useNewUrlParser: true,
      useUnifiedTopology: true,
    });
    await mongoose.connection.dropDatabase();
const testSchema = new mongoose.Schema({name: String});
    testSchema.post('find', (result) => {
        console.log('Hello', result);
    });
    const Test = mongoose.model('Test', testSchema);
    await Test.create({name: 'Daniel'},{name: 'Val'}, {name: 'Daniel'});
    const query = await Test.find({name: 'Daniel'}).cursor();
    query.next().then(doc => {
        console.log('doc', doc);
    });

}
run().catch(err => console.log(err));