docs(typescript): make note about recommending strict mode when using auto typed schemas

[vkarpov15]

Re: #12420

Summary

So strange. The following script fails to compile without --strict.

import { Schema, InferSchemaType } from 'mongoose';

const sightSchema = new Schema({
    name: { type: String, required: true },
    location: { type: [Number], required: false } // all ways to define "location" give the same result
    // location: { type: [Number] }
    // location: [Number]
});

type Sight = InferSchemaType<typeof sightSchema>;

// Property 'location' is missing in type '{ name: string; }' but required in type '{ name: string; location: number[]; }'
const sight: Sight = {
    name: 'Red Square',
};

$ ./node_modules/.bin/tsc  gh-12420.ts 
gh-12420.ts:13:7 - error TS2741: Property 'location' is missing in type '{ name: string; }' but required in type '{ location: unknown[]; name?: unknown; }'.

13 const sight: Sight = {
         ~~~~~


Found 1 error in gh-12420.ts:13

From #12420. This PR makes a note in the docs.

Examples

[hasezoey]

i think the problem more specifically is strictNullChecks, quote:

When strictNullChecks is false, null and undefined are effectively ignored by the language. This can lead to unexpected errors at runtime.
When strictNullChecks is true, null and undefined have their own distinct types and you’ll get a type error if you try to use them where a concrete value is expected.

Typescript: TSConfig Reference