Update sending-bundles.mdx (#636)

comment in code for one backrun tx per bundle

Author: yizhang0901

docs/flashbots-mev-share/searchers/sending-bundles.mdx

@@ -86,7 +86,7 @@ const params: BundleParams = {
     },
     body: [
         {tx: "0x02...", canRevert: false},
-        {tx: "0x02...", canRevert: false},
+        //can only include one backrun tx
     ],
     privacy: {
         hints: {