Add syntax lookup triangle pipe operator

misc_docs/syntax/operators_triangle_pipe.mdx

@@ -0,0 +1,47 @@
+---
+id: "triangle-pipe"
+keywords: [pipe", "triangle", "operator", "function", "argument"]
+name: "|>"
+summary: "This is the `triangle pipe` operator."
+category: "operators"
+---
+
+The `|>` operator passes a value to a function as its last argument.
+
+> Note that this operator has been deprecated. See [Triangle Pipe](/docs/manual/latest/pipe#triangle-pipe-deprecated) for more details.
+
+### Example
+
+<CodeTab labels={["ReScript", "JS Output"]}>
+
+```res
+let dieRoll = size => {
+  Js.Math.random_int(1, size)
+}
+
+let dieRollMessage = (name, value) => {
+  "Hi " ++ name ++ ", you rolled a " ++ Js.Int.toString(value)
+}
+
+let message = dieRoll(6) |> dieRollMessage("Jeremy")
+```
+
+```js
+function dieRoll(size) {
+  return Js_math.random_int(1, size);
+}
+
+function dieRollMessage(name, value) {
+  return "Hi " + name + ", you rolled a " + value.toString();
+}
+
+var message = dieRollMessage("Jeremy", Js_math.random_int(1, 6));
+```
+
+</CodeTab>
+
+Which produces a message such as `Hello Jeremy, you rolled a 3`.
+
+### References
+
+* [Triangle Pipe](/docs/manual/latest/pipe#triangle-pipe-deprecated)