Modify repo "About" to match npm search criteria

[shadowspawn]

The npm documentation for node version managers no longer lists n explicitly and instead links to a search which does not pick up n (/search?q=node+version+manager). I suggest we change the repo About from Node version management to Node.js version manager.

• manager is used heavily by utilities in this domain
• The Node.js convention is Node.js is the project and node is the binary. I think it is appropriate to say Node.js since n manages both node and npm, but could omit as less familiar although more accurate.

[mrienstra]

Huh, it would be nicer if that link went to:
https://nodejs.org/en/download/package-manager/all