Add note for Windows limitation on datetime format string

Author: neolee

p2-6-string-data.ipynb

@@ -558,7 +558,7 @@
     "print(\"月：\", t.strftime(\"%m\"))\n",
     "print(\"日：\", t.strftime(\"%d\"))\n",
     "print(\"完整日期：\", t.strftime(\"%Y-%m-%d\"))\n",
-    "print(\"压缩版日期：\", t.strftime(\"%Y-%-m-%-d\"))\n",
+    "print(\"压缩版日期：\", t.strftime(\"%Y-%-m-%-d\")) # 压缩格式 %-m 和 %-d 不被 Windows 支持，所以这一句在 Windows 环境下会出错\n",
     "print(\"24小时制时间：\", t.strftime(\"%H:%M:%S\"))\n",
     "print(\"12小时制时间：\", t.strftime(\"%I:%M:%S %p\"))\n",
     "print(\"日期加时间：\", t.strftime(\"%Y-%m-%d %H:%M:%S\"))\n",