[core] Set required yarn version (#12864)
[core] Set required yarn version (#12864)

* [core] Set required yarn version

Before 1.4.0 bin commands could not be found when executed from
a workspace. See yarnpkg/yarn#4848

* Revert "[core] Set required yarn version"

This reverts commit e6260e317a23ec7a5ad20de54258f1986bfa7284.

Netlify uses 1.3.2 which has the same issue. This also limits
users not just contributors.

* [core] Add note about build prerequisites

* Update CONTRIBUTING.md

Kagami/material-ui,kybarg/material-ui,oliviertassinari/material-ui,oliviertassinari/material-ui,Kagami/material-ui,kybarg/material-ui,Kagami/material-ui,rscnt/material-ui,kybarg/material-ui,callemall/material-ui,mui-org/material-ui,Kagami/material-ui,oliviertassinari/material-ui,allanalexandre/material-ui,mbrookes/material-ui,callemall/material-ui,mbrookes/material-ui,mui-org/material-ui,callemall/material-ui,rscnt/material-ui,lgollut/material-ui,rscnt/material-ui,mui-org/material-ui,kybarg/material-ui,mbrookes/material-ui,callemall/material-ui