README: Add packaging status badge #1446

Job	Run time
cargo-c	31s
Build+test (clang, stable, ubuntu-latest)	50s
Build+test (clang, beta, ubuntu-latest)	58s
Clippy	20s
Build+test (clang, nightly, ubuntu-latest)	55s
Clang Tidy	9s
Clippy nightly (optional)	18s
Build+test (clang, 1.61.0, ubuntu-latest)	2m 2s
Build+test (gcc, stable, ubuntu-latest)	48s
ensure-header-updated	1m 3s
Build+test (gcc, beta, ubuntu-latest)	50s
Format	13s
Build+test (gcc, nightly, ubuntu-latest)	50s
Check for documentation errors	19s
Build+test (gcc, 1.61.0, ubuntu-latest)	1m 57s
Check minimum versions	40s
Build+test (macos-latest, clang, stable)	1m 47s
Miri	53s
Windows CMake, Debug configuration	2m 17s
Windows CMake, Release configuration	2m 4s
Valgrind	1m 8s
	20m 52s

Provide feedback