Update misc_docs/syntax/operators_pipe.mdx

Co-authored-by: Patrick Ecker <[email protected]>

Author: kevanstannard

misc_docs/syntax/operators_pipe.mdx

@@ -40,6 +40,37 @@ var message = dieRollMessage(Js_math.random_int(1, 6), "Marshall");
 
 Which produces a message such as `Hello Marshall, you rolled a 3`.
 
+You can also explicitly define the argument position of a piped value by using the `_` placeholder: 
+
+<CodeTab labels={["ReScript", "JS Output"]}>
+
+```res example
+let logMsg = (user: string, datestr: string, msg: string): unit => {
+  Js.log(`${user}|${datestr}|${msg}`)
+}
+
+let datestr = "01-01-2021"
+let user = "admin"
+
+// Here, we put the result of toUpperCase into the last position
+// denoted with an _
+Js.String2.toUpperCase("example message")->logMsg(user, datestr, _)
+```
+
+```js
+function logMsg(user, datestr, msg) {
+  console.log(user + "|" + datestr + "|" + msg);
+  
+}
+
+var datestr = "01-01-2021";
+
+var user = "admin";
+
+logMsg(user, datestr, "example message".toUpperCase());
+```
+
+</CodeTab>
 ### References
 
 * [Pipe](/docs/manual/latest/pipe)