sassw: include time taken for rebuilding css

bin/sassw

@@ -11,6 +11,7 @@ import os
 import pyinotify
 import subprocess
 import sys
+import time
 
 filename = sys.argv[1]
 
@@ -26,8 +27,10 @@ class EventManager(pyinotify.ProcessEvent):
         if event.pathname in sources:
             filename = os.path.basename(event.pathname)
             print(f'{filename} changed, building', end='')
+            t0 = time.time()
             build()
-            print('.')
+            elapsed_time = time.time() - t0
+            print(' (%.2fs)' % (time.time() - t0))
 
 build()
 wm = pyinotify.WatchManager()