add type assertion for useState thanks @priscilaandreani

closes typescript-cheatsheets/react#403

Author: secretsuperstar1109

Diff for: docs/basic/getting-started/hooks.md

@@ -7,7 +7,7 @@ Hooks are [supported in `@types/react` from v16.8 up](https://github.com/Definit
 
 ## useState
 
-Type inference works very well most of the time:
+Type inference works very well for simple values:
 
 ```tsx
 const [val, toggle] = React.useState(false);
@@ -22,10 +22,21 @@ However, many hooks are initialized with null-ish default values, and you may wo
 ```tsx
 const [user, setUser] = React.useState<IUser | null>(null);
 
+// later...
+setUser(newUser); 
+```
+
+You can also use type assertions if a state is initialized soon after setup and always has a value after:
+
+```tsx
+const [user, setUser] = React.useState<IUser>({} as IUser);
+
 // later...
 setUser(newUser);
 ```
 
+This temporarily "lies" to the TypeScript compiler that `{}` is of type `IUser`. You should follow up by setting the `user` state — if you don't, the rest of your code may rely on the fact that `user` is of type `IUser` and that may lead to runtime errors.
+
 ## useReducer
 
 You can use [Discriminated Unions](https://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes-func.html#discriminated-unions) for reducer actions. Don't forget to define the return type of reducer, otherwise TypeScript will infer it.