Documentation: Clarify that runtime.sendMessage does not notify itself

extensions/common/api/runtime.json

Index: extensions/common/api/runtime.json
diff --git a/extensions/common/api/runtime.json b/extensions/common/api/runtime.json
index 0c28293971f44609e516d657973a977061b45002..893ffc0fd9a90f9685505c053aaa67be34eafdcb 100644
--- a/extensions/common/api/runtime.json
+++ b/extensions/common/api/runtime.json
@@ -326,7 +326,7 @@
         "type": "function",
         "nocompile": true,
         "allowAmbiguousOptionalArguments": true,
-        "description": "Sends a single message to event listeners within your extension/app or a different extension/app. Similar to $(ref:runtime.connect) but only sends a single message, with an optional response. If sending to your extension, the $(ref:runtime.onMessage) event will be fired in each page, or $(ref:runtime.onMessageExternal), if a different extension. Note that extensions cannot send messages to content scripts using this method. To send messages to content scripts, use $(ref:tabs.sendMessage).",
+        "description": "Sends a single message to event listeners within your extension/app or a different extension/app. Similar to $(ref:runtime.connect) but only sends a single message, with an optional response. If sending to your extension, the $(ref:runtime.onMessage) event will be fired in every frame of your extension (except for the sender's frame), or $(ref:runtime.onMessageExternal), if a different extension. Note that extensions cannot send messages to content scripts using this method. To send messages to content scripts, use $(ref:tabs.sendMessage).",
         "parameters": [
           {"type": "string", "name": "extensionId", "optional": true, "description": "The ID of the extension/app to send the message to. If omitted, the message will be sent to your own extension/app. Required if sending messages from a web page for <a href=\"manifest/externally_connectable.html\">web messaging</a>."},
           { "type": "any", "name": "message", "description": "The message to send. This message should be a JSON-ifiable object." },