Improve contributing guide.

CONTRIBUTING.md

@@ -111,6 +111,30 @@ bundle exec rspec --only-failures
 bundle exec rspec --next-failure
 ```
 
+## Project Website
+
+The source code for https://block.github.io/elasticgraph/ lives in [config/site](code/site). To serve it locally, run:
+
+```
+bundle exec rake site:serve
+```
+
+Then visit http://localhost:4000/elasticgraph/ in your brower. Local edits to the site will be reflected when you reload a page.
+
+### API Documentation
+
+ElasticGraph's Ruby code is documented using [YARD](https://yardoc.org/). You can view the rendered API docs in the context of the
+project website using the same `site:serve` rake task (just visit http://localhost:4000/elasticgraph/docs/main/). However, that task
+fully regenerates the documentation from scratch and it's not very quick. If you're working on multiple changes to the API documentation,
+you'll get a faster feedback loop using the `site:preview_docs:[gem name]` tasks. For example, to preview the docs of
+[elasticgraph-schema_definition](elasticgraph-schema_definition), run:
+
+```bash
+bundle exec rake site:preview_docs:elasticgraph-schema_definition
+```
+
+Then visit http://localhost:8808/. The preview task will rebuild the parts of the generated docs impacted by your edits, and is quite fast.
+
 ---
 
 ## Communications
@@ -122,21 +146,23 @@ Anyone from the community is welcome (and encouraged!) to raise issues via
 
 ### Discussions
 
-Design discussions and proposals take place in our [discord](https://discord.gg/8m9FqJ7a7F).
+Design discussions and proposals take place on [GitHub discussions](https://github.com/block/elasticgraph/discussions).
+We advocate an asynchronous, written discussion model - so write up your thoughts and invite the community to join in!
 
-We advocate an asynchronous, written debate model - so write up your thoughts and invite the community to join in!
+In addition, we have a [discord channel](https://discord.gg/8m9FqJ7a7F) for synchronous communication. Discord is best
+for questions and general conversation.
 
 ### Continuous Integration
 
-Build and Test cycles are run on every commit to every branch on [GitHub Actions](https://github.com/block/elasticgraph/actions).
+Build and test cycles are run on every commit to every branch on [GitHub Actions](https://github.com/block/elasticgraph/actions).
 
 ## Contribution
 
 We review contributions to the codebase via GitHub's Pull Request mechanism. We have
 the following guidelines to ease your experience and help our leads respond quickly
 to your valuable work:
 
-* Start by proposing a change either in Issues (most appropriate for small
+* Start by proposing a change either on Discord (most appropriate for small
   change requests or bug fixes) or in Discussions (most appropriate for design
   and architecture considerations, proposing a new feature, or where you'd
   like insight and feedback)