Add comment for manual path prepend

src/offline/build3.sh

@@ -16,8 +16,10 @@ host_gadi()
    module add intel-compiler/2019.5.281
    module add netcdf/4.6.3
    # This is required so that the netcdf-fortran library is discoverable by
-   # pkg-config:
-   PKG_CONFIG_PATH=${NETCDF_BASE}/lib/Intel/pkgconfig/:$PKG_CONFIG_PATH
+   # pkg-config (Note, we manually prepend to PKG_CONFIG_PATH instead of
+   # using `module prepend-path` so that we can invoke this script successfully
+   # in benchcab):
+   export PKG_CONFIG_PATH=${NETCDF_BASE}/lib/Intel/pkgconfig/:$PKG_CONFIG_PATH
 
    if ! pkg-config --exists netcdf-fortran; then
        echo ''