Add nodenv support to Node.js module

- Implementation from https://github.com/sorin-ionescu/prezto/pull/1001
- Documentation from https://github.com/sorin-ionescu/prezto/pull/1178

modules/node/README.md

@@ -10,6 +10,13 @@ nvm
 [nvm][5] allows for managing multiple, isolated Node.js installations in the
 home directory.
 
+nodenv
+------
+
+[nodenv][6] does one thing well. nodenv is concerned solely with switching
+Node versions. It's simple and predictable, Just Works, and is rock solid in
+production. nodenv is forked from the popular [rbenv][7].
+
 Functions
 ---------
 
@@ -43,3 +50,5 @@ Authors
 [3]: http://nodejs.org/api
 [4]: https://github.com/sorin-ionescu/prezto/issues
 [5]: https://github.com/creationix/nvm
+[6]: https://github.com/nodenv/nodenv
+[7]: https://github.com/sstephenson/rbenv