doc: add links to source code in docs

[aw-davidson]

📗 API Reference Docs Problem

• Version: N/A
• Platform: N/A
• Subsystem: N/A

Location

On every module docs page

Affected URL(s):

• https://nodejs.org/api/*

Problem description

It would be nice to have links to source code below the title of each module. For an example, look at pythons documentation for the heapq module: https://docs.python.org/3/library/heapq.html. So for node Buffer it would look like:

Buffer

Stability: 2 - Stable

Source Code: lib/buffer.js

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• I would like to work on this issue and submit a pull request.