android build: update README to newer build.sh syntax

contrib/android/Readme.md

@@ -17,16 +17,16 @@ similar system.
 
 2. Build binaries
 
+    The build script takes a few arguments. To see syntax, run it without providing any:
     ```
     $ ./build.sh
     ```
+    For development, consider e.g. `$ ./build.sh kivy arm64-v8a debug`
+
     If you want reproducibility, try instead e.g.:
     ```
-    $ ELECBUILD_COMMIT=HEAD ELECBUILD_NOCACHE=1 ./build.sh release-unsigned
+    $ ELECBUILD_COMMIT=HEAD ELECBUILD_NOCACHE=1 ./build.sh kivy all release-unsigned
     ```
-    
-    Note: `build.sh` takes an optional parameter which can be
-    `release`, `release-unsigned`, or `debug` (default).
 
 3. The generated binary is in `./dist`.
 
@@ -37,7 +37,7 @@ Every user can verify that the official binary was created from the source code
 repository.
 
 1. Build your own binary as described above.
-   Make sure you don't build in `debug` mode (which is the default!),
+   Make sure you don't build in `debug` mode,
    instead use either of `release` or `release-unsigned`.
    If you build in `release` mode, the apk will be signed, which requires a keystore
    that you need to create manually (see source of `make_apk` for an example).

contrib/android/make_apk

@@ -55,7 +55,7 @@ elif [[ "$3" == "release-unsigned" ]] ; then
     # do release build, but do not sign the APKs.
     TARGET="release"
 elif [[ "$3" == "debug" ]] ; then
-    # do debug build; the default.
+    # do debug build.
     TARGET="apk"
     export P4A_DEBUG_KEYSTORE="$CONTRIB_ANDROID"/android_debug.keystore
     export P4A_DEBUG_KEYSTORE_PASSWD=unsafepassword