Provide android cross-compile docker example

[AndreyMlashkin]

Description of Problem, Request, or Question

Please, provide a modern way of cross compiling from Linux to Android.
The best example would be a valid docker image.

For now, there are only deprecated images for cross-compilation.

[uilianries]

Done in the official documentation: https://docs.conan.io/en/latest/integrations/cross_platform/android.html#using-docker-images

[AndreyMlashkin]

awesome

[uilianries]

@AndreyMlashkin Tell if it's not clear enough, there is always margin for improvements in the documentation.