Suggest using --user when the install directory isn't writable.

Fixes #1540.

--
Change-Id: I0f16bde6496f2abef8ba3d3562e62a1534c177ca
Reviewed-on: https://bazel-review.googlesource.com/#/c/4081/
MOS_MIGRATED_REVID=127960571
diff --git a/scripts/packages/template_bin.sh b/scripts/packages/template_bin.sh
index 5323946..ceb58c8 100755
--- a/scripts/packages/template_bin.sh
+++ b/scripts/packages/template_bin.sh
@@ -86,6 +86,7 @@
   [ -w "${file}" ] || {
     echo >&2
     echo "The Bazel installer must have write access to $1!" >&2
+    echo "Consider using the --user flag to install Bazel under $HOME/bin instead." >&2
     echo >&2
     usage
   }