Update Android debugging docs to suggest `adb logcat`.

I wasn't able to see my LOG(INFO) output when running the test
binary with `logcat -v` added, but a colleague suggested `adb logcat`,
which worked. This CL updates the Android debugging docs to suggest
`adb logcat` for viewing printed log lines.

Change-Id: Iec2152b9fb5ca265239e7515482ff7be823eddca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023390
Commit-Queue: David Van Cleve <davidvc@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736386}

docs/android_debugging_instructions.md

@@ -25,6 +25,9 @@ with:
 out/Default/bin/chrome_public_apk logcat [-v]  # Use -v to show logs for other processes
 ```
 
+If this doesn't display the logs you're looking for, try `adb logcat` with your system `adb`
+or the one in `//third_party/android_sdk/`.
+
 ### Warnings for Blink developers
 *   **Do not use fprintf or printf debugging!** This does not
     redirect to logcat.