Node: Update fs.md

[muzhaqi16]

I thought it was the same thing as well but unfortunately when I use require('fs/promises') I do receive an error message on my node environment but not if I use the second option.

Error: Cannot find module 'fs/promises'
Require stack:

My node version is v12.18.3

_Originally posted by @muzhaqi16 in https://github.com/nodejs/node/pull/35726#issuecomment-713544608_

[aduh95]

The current documentation is only true for Node.js 14+. For Node.js 12, please check out https://nodejs.org/docs/latest-v12.x/api/fs.html#fs_fs_promises_api

For info, here is the support table for those features:

| Node.js version range | require('fs/promises') | require('fs').promises |
| - | - | - |
| v10.0.0 | ✅ | ❌ |
| ≥v10.1.0 <14.0.0 | ❌ | ✅ |
| ≥14.0.0 | ✅ | ✅ |

Maybe we could add an history section in the docs to clarify what support users can expect.