Summary:
**what is the change?:**
Adding a document linking to the Facebook Open Source Code of Conduct,
for visibility and to meet Github community standards.
**why make this change?:**
Facebook Open Source provides a Code of Conduct statement for all
projects to follow.
Metro already links to this Code of Conduct in the CONTRIBUTING, which is
great!
Exposing the COC via a separate markdown file is a standard being
promoted by Github via the Community Profile in order to meet their Open
Source Guide's recommended community standards.
As you can see, adding this file will complete [Metro's Community Profile](https://github.com/facebook/metro-bundler/community)
checklist and increase the visibility of our COC.
**test plan:**
Viewing it on my branch -
**issue:**
internal task t23481323
Closes https://github.com/facebook/metro-bundler/pull/93
Reviewed By: cpojer
Differential Revision: D6395546
Pulled By: flarnie
fbshipit-source-id: dacc85abed53cec3e6200daa8fe139cd6c53b7a0
