doc: Add link for ECMAScript 2015

PR-URL: #17317
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>

Author: smatsu-hl

doc/api/buffer.md

@@ -4,7 +4,7 @@
 
 > Stability: 2 - Stable
 
-Prior to the introduction of [`TypedArray`] in ECMAScript 2015 (ES6), the
+Prior to the introduction of [`TypedArray`] in [`ECMAScript 2015`] (ES6), the
 JavaScript language had no mechanism for reading or manipulating streams
 of binary data. The `Buffer` class was introduced as part of the Node.js
 API to make it possible to interact with octet streams in the context of things
@@ -211,7 +211,7 @@ changes:
 -->
 
 `Buffer` instances are also [`Uint8Array`] instances. However, there are subtle
-incompatibilities with the TypedArray specification in ECMAScript 2015.
+incompatibilities with the TypedArray specification in [`ECMAScript 2015`].
 For example, while [`ArrayBuffer#slice()`] creates a copy of the slice, the
 implementation of [`Buffer#slice()`][`buf.slice()`] creates a view over the
 existing `Buffer` without copying, making [`Buffer#slice()`][`buf.slice()`] far
@@ -291,7 +291,7 @@ function:
 
 ## Buffers and ES6 iteration
 
-`Buffer` instances can be iterated over using the ECMAScript 2015 (ES6) `for..of`
+`Buffer` instances can be iterated over using the [`ECMAScript 2015`] (ES6) `for..of`
 syntax.
 
 Example:
@@ -2755,4 +2755,5 @@ This value may depend on the JS engine that is being used.
 [RFC1345]: https://tools.ietf.org/html/rfc1345
 [RFC4648, Section 5]: https://tools.ietf.org/html/rfc4648#section-5
 [WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/
+[`ECMAScript 2015`]: https://www.ecma-international.org/ecma-262/6.0/index.html
 [iterator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols