Add documentation link to nvexeca

[ehmicky]

This adds a link to nvexeca in the Related section.

nvexeca is a thin wrapper around Execa which adds the possibility to choose a Node.js version to run the command.

In a nutshell it simply:

• downloads the Node.js binary from https://nodejs.org (unless already cached)
• then calls execa(command, args, { execPath: nodeBinaryPath })

Instead of:

const execa = require('execa')
execa(command, args, options)

One would do (to run Node 10):

const nvexeca = require('nvexeca')
nvexeca('10', command, args, options)