Add documentation to demonstrate code splitting on server side apps.

This is with reference to this link. Though i admit the documentation is pretty lucid, i feel a section can also be made for code splitting with server sided react apps. This is particularly tricky as correct bundles have to be utilised / picked up on both server and client side. This will be particularly useful for someone who is not using next / gatsby and is trying to use their own webpack config. Alternatively we can also show the above using react-loadable. I know the docs here are pertaining to just react, but adding this section may be helpful. If okay i'm cool with submitting a PR.

Comece por content/docs/code-splitting.md e, em seguida, analise o cenário da issue sobre React no lado do servidor e uma configuração personalizada do webpack. Decida se a documentação deve abordar a seleção personalizada de bundles de servidor/cliente ou demonstrar react-loadable. O trabalho estará concluído quando a documentação explicar claramente a divisão de código no lado do servidor para apps que não usam Next nem Gatsby.