hostinfo: update SetPackage doc with new Android values (#13537)

Fixes tailscale/corp#23283

Signed-off-by: kari-ts <kari@tailscale.com>

hostinfo/hostinfo.go

@@ -200,8 +200,13 @@ func SetFirewallMode(v string) { firewallMode.Store(v) }
 
 // SetPackage sets the packaging type for the app.
 //
-// As of 2022-03-25, this is used by Android ("nogoogle" for the
-// F-Droid build) and tsnet (set to "tsnet").
+// For Android, the possible values are:
+// - "googleplay": installed from Google Play Store.
+// - "fdroid": installed from the F-Droid repository.
+// - "amazon": installed from the Amazon Appstore.
+// - "unknown": when the installer package name is null.
+// - "unknown$installerPackageName": for unrecognized installer package names, prefixed by "unknown".
+// Additionally, tsnet sets this value to "tsnet".
 func SetPackage(v string) { packagingType.Store(v) }
 
 // SetApp sets the app type for the app.