Improve gbuild help text with PARALLELISM env var.
Improve gbuild help text with PARALLELISM env var.

Change-Id: I30c9700127d04aee200386c94307a45da41b0025

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core