health: Update README.md for SELinux rule example

process is executed, especially if a device-specific `libhealthd` is used

and/or device-specific storage related APIs are implemented.

Example (assuming that your health AIDL service runs in domain

`hal_health_tuna`:

```text

type hal_health_tuna, domain;

hal_server_domain(hal_health_tuna, hal_health)

type hal_health_tuna_exec, exec_type, vendor_file_type, file_type;

# allow hal_health_tuna ...;

```

If you did not define a separate domain, the domain is likely

`hal_health_default`. The device-specific rules for it is likely at

`device/<manufacturer>/<device>/sepolicy/vendor/hal_health_default.te`.

In this case, the aforementioned SELinux rules and types has already been

defined. You only need to add device-specific permissions.

```text

# allow hal_health_default ...;

```

### Implementing charger {#charger}