docs:(content/docs/strict-mode.md) fixed the documentation around strict mode double invoking function component bodies but only those which use hooks

[vivek12345]

Currently the documentation says it will double invoke function component bodies in strict mode. This can get slightly confusing in a scenario like this sandbox
https://codesandbox.io/s/inspiring-water-892dq?file=/src/App.js

Here only the function component body of H1 is being double invoked as it has a call to a react hook useEffect.

Functional component H2 in above sandbox is only being called once.

This is the reason I feel adding a little more context around the documentation for double invoking of functional component bodies will help the users.

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