extend readme with information on running buildozer

README.md

@@ -2,23 +2,31 @@
 
 Mobile app, client of flock server.
 
-
 ## Development
 
 Install dependencies like so:
 
-```
     $ pip install -r requirements.txt
+
+[It might be necessary](https://github.com/kivy/buildozer/issues/769) to
+manually download an android NDK. If so, go to [ndk
+downloads](https://developer.android.com/ndk/downloads/) and get the appropiate
+version. Put it somewhere (it could be inside this repository) and adjust
+`android.ndk_path` in `buildozer.spec`. Relative paths are valid, so this is a
+sensible value:
+
+```ini
+# (str) Android NDK directory (if empty, it will be automatically downloaded.)
+android.ndk_path = ./android-ndk-r25b-linux
 ```
 
 ## Test building
 
-Kivy apps are easily deployed and tested with [buildozer](https://buildozer.readthedocs.io/en/latest/quickstart.html#init-and-build-for-android).
+Kivy apps are easily deployed and tested with
+[buildozer](https://buildozer.readthedocs.io/en/latest/quickstart.html#init-and-build-for-android).
 
 This command will compile the app, transfer it to a usb-connected
 device and run it. Logs are shown on the console, hence the grep
 python.
 
-```
     $ buildozer -v android debug deploy run logcat | grep python
-```