Tell people how to find zipalign

Summary: Hopefully this helps

Reviewed By: satnam6502

Differential Revision: D3181313

fb-gh-sync-id: 1f5704f090a4ff954edad19017c30a3a03ac4a76
fbshipit-source-id: 1f5704f090a4ff954edad19017c30a3a03ac4a76

README.md

@@ -90,6 +90,19 @@ input.  Enjoy!
 
 # FAQ
 
+## I'm getting "Couldn't find zipalign. See README.md to resolve this"
+
+`zipalign` is an optimization step that is bundled with the Android SDK.  You
+need to tell redex where to find it.  For example, if you installed the SDK at
+`/path/to/android/sdk`, try:
+```
+ANDROID_SDK=/path/to/android/sdk redex [... arguments ...]
+```
+You can alternatively add `zipalign` to your PATH, for example:
+```
+PATH=/path/to/android/sdk/build-tools/xx.y.zz:$PATH redex [... arguments ...]
+```
+
 ## How does this compare to ProGuard?
 
 ReDex is conceptually similar to ProGuard, in that both optimize bytecode.

redex.py

@@ -477,7 +477,7 @@ def zipalign(unaligned_apk_path, output_apk_path):
         subprocess.check_call(zipalign +
                               ['4', unaligned_apk_path, output_apk_path])
     except:
-        print("Couldn't find zipalign.  Your APK may not be fully optimized.")
+        print("Couldn't find zipalign. See README.md to resolve this.")
         shutil.copy(unaligned_apk_path, output_apk_path)
     os.remove(unaligned_apk_path)