doc: Add some descriptions for runc sandbox and microvm sandbox #692

Job	Run time
tests (vmm/sandbox, --all-features)	3m 11s
checks (vmm/sandbox, --all-features)	4m 43s
tests (vmm/task, --all-features)	2m 40s
checks (vmm/task, --all-features)	4m 7s
tests (shim, --all-features)	2m 41s
checks (shim, --all-features)	4m 21s
tests (quark, --all-features)	2m 39s
checks (quark, --all-features)	4m 14s
tests (runc, --all-features)	2m 45s
checks (runc, --all-features)	4m 14s
tests (wasm, --features=wasmedge, 0.11.2)	2m 47s
checks (wasm, --features=wasmedge, 0.11.2)	4m 30s
checks (wasm, --features=wasmtime)	5m 5s
tests (wasm, --features=wasmtime)	3m 19s
	51m 16s

Provide feedback