Fix sentence in build/README.md
Fix sentence in build/README.md

MichaelMaar/concrete5,matt9mg/concrete5,avdevs/concrete5,MichaelMaar/concrete5,matt9mg/concrete5,avdevs/concrete5,TimDix/concrete5,matt9mg/concrete5,TimDix/concrete5,TimDix/concrete5,avdevs/concrete5,MichaelMaar/concrete5