doc: Add contribution philosophy doc

CONTRIBUTING.md

@@ -0,0 +1,66 @@
+# **node-addon-api** Contribution Philosophy
+
+The **node-addon-api** team loves contributions. There are many ways in which you can
+contribute to **node-addon-api**:
+- Source code fixes
+- Additional tests
+- Documentation improvements
+- Joining the N-API working group and participating in meetings
+
+## Source changes
+
+**node-addon-api** is meant to be a thin convenience wrapper around N-API. With this
+in mind, contributions of any new APIs that wrap around a core N-API API will
+be considered for merge. However, changes that wrap existing **node-addon-api**
+APIs are encouraged to instead be provided as an ecosystem module. The
+**node-addon-api** team is happy to link to a curated set of modules that build on
+top of **node-addon-api** if they have broad usefulness to the community and promote
+a recommended idiom or pattern.
+
+### Rationale
+
+The N-API team considered a couple different approaches with regards to changes
+extending **node-addon-api**
+- Larger core module - Incorporate these helpers and patterns into **node-addon-api**
+- Extras package - Create a new package (strawman name '**node-addon-api**-extras')
+that contain utility classes and methods that help promote good patterns and
+idioms while writing native addons with **node-addon-api**.
+- Ecosystem - Encourage creation of a module ecosystem around **node-addon-api**
+where folks can build on top of it.
+
+#### Larger Core
+This is probably our simplest option in terms of immediate action needed. It
+would involve landing any open PRs against **node-addon-api**, and continuing to
+encourage folks to make PRs for utility helpers against the same repository.
+
+The downside of the approach is the following:
+- Less coherency for our API set
+- More maintenance burden on the N-API WG core team.
+
+#### Extras Package
+This involves us spinning up a new package which contains the utility classes
+and methods. This has the benefit of having a separate module where helpers
+which make it easier to implement certain patterns and idioms for native addons
+easier.
+
+The downside of this approach is the following:
+- Potential for confusion - we'll need to provide clear documentation to help the
+community understand where a particular contribution should be directed to (what
+belongs in **node-addon-api** vs **node-addon-api-extras**)
+- Need to define the level of support/API guarantees
+- Unclear if the maintenance burden on the N-API WG is reduced or not
+
+#### Ecosystem
+This doesn't require a ton of up-front work from the N-API WG. Instead of
+accepting utility PRs into **node-addon-api** or creating and maintaining a new
+module, the WG will encourage the creation of an ecosystem of modules that
+build on top of **node-addon-api**, and provide some level of advertising for these
+modules (listing them out on the repository/wiki, using them in workshops/tutorials
+etc).
+
+The downside of this approach is the following:
+- Potential for lack of visibility - evangelism and education is hard, and module
+authors might not find right patterns and instead implement things themselves
+- There might be greater friction for the N-API WG in evolving APIs since the
+ecosystem would have taken dependencies on the API shape of **node-addon-api**
+

README.md

@@ -159,6 +159,11 @@ Take a look and get inspired by our **[test suite](https://github.com/nodejs/nod
 
 <a name="resources"></a>
 
+## **Contributing**
+
+We love contributions from the community to **node-addon-api**. 
+See [CONTRIBUTING.md](CONTRIBUTING.md) for more details on our philosophy around extending this module.
+
 ### **More resource and info about native Addons**
 - **[C++ Addons](https://nodejs.org/dist/latest/docs/api/addons.html)**
 - **[N-API](https://nodejs.org/dist/latest/docs/api/n-api.html)**