A little help message for Android viewer's build dir

I think that I've mis-used out/Debug multiple times to build Android
viewer. Maybe this message would help me and others in the future.

No-Try: true
Docs-Preview: https://skia.org/?cl=18587
Bug: skia:
Change-Id: I810920a0ca4aa8a46dd58b35966e08513520953c
Reviewed-on: https://skia-review.googlesource.com/18587
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>
1 file changed