CONTRIBUTING.md could use additional info on dev. environment requirements.

[WesTyler]

I am trying to add some tests around the serialization functions (may PR if I can replicate behavior).

I followed the guidelines in CONTRIBUTING.md and have so far run into the following roadblocks that were not readily apparent:

1. Must be in Node version >=5.x OR be using Node v4.x with the --harmony flag

wtyler:elasticsearch-js (master *)$ node --version
v4.5.0
wtyler:elasticsearch-js (master *)$ grunt test
Loading "Gruntfile.js" tasks...ERROR
>> SyntaxError: Unexpected token ...
Warning: Task "test" not found. Use --force to continue.

Aborted due to warnings.

2. Must have JDK installed to utilize java command-line tool. (Semi-related side note, the dialogue box that pops up in this case does not correctly direct you to the JDK install page...)

Warning: Command failed: /.../.../elasticsearch-js/esvm/branch-5.2/bin/elasticsearch -h
No Java runtime present, requesting install.
 Use --force to continue.

Aborted due to warnings.

Would you be open to a documentation-only PR to amend the CONTRIBUTING.md with the below information?

3. When you are ready, run the test suite

1. Install dev dependencies.

npm install

2. Ensure that your development environment meets the below minimum requirements.

• Node version >=5.x, or Node version 4.x with --harmony flag.
• Java Developer Kit. Tests make use of the java command-line tool.
• Global install of Grunt command-line tool:

  npm install -g grunt-cli

3. Run the tests.

[spalger]

Yeah, I'd totally be interested in a PR. I'd call out nvm, avn and jabba and would probably structure it similar to the kibana contributing doc.

[stale]

We understand that this might be important for you, but this issue has been automatically marked as stale because it has not had recent activity either from our end or yours.
It will be closed if no further activity occurs, please write a comment if you would like to keep this going.

Note: in the past months we have built a new client, that has just landed in master. If you want to open an issue or a pr for the legacy client, you should do that in https://github.com/elastic/elasticsearch-js-legacy

[delvedor]

Closed in f260549 and #794.