doc: move numCPUs require to top of file in `cluster` CJS example
There is one particular CJS
example in the Cluster
docs where there's a require statement inside a condition. I've moved the statement to the top of the file to be consistent with it's ESM
counterpart and also the rest of the examples like the first one or the one in worker.isDead()
.
It follows the same order in which it's being imported on the rest of the examples.
Best regards,