Update readme

Author: valotas

README.md

@@ -1,5 +1,9 @@
 # Docker image with Android SDK and Flutter
 
+Based on [`openjdk:8-slim`](https://hub.docker.com/_/openjdk/) and the work of
+[Álvaro S.](https://github.com/alvr/alpine-android) on installing the android
+sdk.
+
 ## Building and running
 
 ```
@@ -9,7 +13,9 @@ docker run -it --entrypoint=/bin/bash [image-name]
 
 ## Bitbucket Pipelines
 
-This image can be used to test and build Android APKs developed with Flutter. Here is an example `bitbucket-pipelines.yml` for Bitbucket Pipelines including caches for gradle and gradlewrapper:
+This image can be used to test and build Android APKs developed with Flutter.
+Here is an example `bitbucket-pipelines.yml` for Bitbucket Pipelines including
+caches for gradle and gradlewrapper:
 
 ```
 image: valotas/lokali-build:version-1