Add window context function example

Signed-off-by: xiaolong.ran <[email protected]>

Author: wolfstudy

site2/docs/window-functions-context.md

@@ -32,7 +32,8 @@
       "functions-develop",
       "functions-debug",
       "functions-deploy",
-      "functions-cli"
+      "functions-cli",
+      "window-functions-context"
     ],
     "Pulsar IO": [
       "io-overview",