Include system RAM size in usage report

cmd/syncthing/memsize_darwin.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"errors"
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+func memorySize() (uint64, error) {
+	cmd := exec.Command("sysctl", "hw.memsize")
+	out, err := cmd.Output()
+	if err != nil {
+		return 0, err
+	}
+	fs := strings.Fields(string(out))
+	if len(fs) != 2 {
+		return 0, errors.New("sysctl parse error")
+	}
+	bytes, err := strconv.ParseUint(fs[1], 10, 64)
+	if err != nil {
+		return 0, err
+	}
+	return bytes, nil
+}