Add prompt about importing local sheet

shared_sheets.json

@@ -1,5 +1,13 @@
 {
   "sheets": [{
+    "name": "雨的印记（Kiss the Rain)",
+    "file": "Kiss_the_Rain.txt",
+    "author": "酷安@你们很有趣呢",
+    "desc": "酷安酷友<a href=http://www.coolapk.com/u/2416229>酷安@你们很有趣呢<a/>分享乐谱 雨的印记（Kiss the Rain)\n初始手编作，更多谱子即将到来。",
+    "bpm" : 225,
+    "suggested_instrument": 1,
+    "pitchLevel": 9
+  }, {
     "name": "The Right Path",
     "file": "The_Right_Path.txt",
     "author": "酷安@夏川丶呇",