Update and add READMEs #74

Job	Run time
formatting	8s
Check MSRV (1.64.0)	3m 19s
clippy	40s
Host-side tests (ubuntu-latest, stable)	41s
Host-side tests (ubuntu-latest, nightly)	53s
Build-test docs (ubuntu-latest, stable)	38s
Build-test docs (ubuntu-latest, nightly)	47s
Build apk (ubuntu-latest, stable, armv7-linux-androideabi)	2m 4s
Build apk (ubuntu-latest, stable, aarch64-linux-android)	1m 51s
Build apk (ubuntu-latest, stable, i686-linux-android)	2m 12s
Build apk (ubuntu-latest, stable, x86_64-linux-android)	1m 54s
Build apk (ubuntu-latest, nightly, armv7-linux-androideabi)	2m 19s
Build apk (ubuntu-latest, nightly, aarch64-linux-android)	2m 30s
Build apk (ubuntu-latest, nightly, i686-linux-android)	4m 45s
Build apk (ubuntu-latest, nightly, x86_64-linux-android)	1m 54s
Build apk (windows-latest, stable, aarch64-linux-android)	9m 20s
Build apk (windows-latest, stable, x86_64-linux-android)	8m 6s
hello_world example on emulator (ubuntu-latest)	2m 37s
hello_world example on emulator (windows-latest)	7m 31s
hello_world example on emulator (local)	6m 6s
	1h 0m 15s

Provide feedback