README.Android: document requirements for an all-symbol build
README.Android: document requirements for an all-symbol build

Change-Id: I945b9833dee3a47cf23760b3f22917731a879e12

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