Expand README

README.md

 # marketo-tools
 
-This is a simple Sinatra application that receives GitLab.com sign-up hooks and
-passes the relevant information to Marketo leads.
+This is a simple Sinatra application that receives several web hooks and
+forwards the relevant information to Marketo via its REST API.
+
+## Handlers
+
+### License for Free Trial
+
+```text
+"Free Trial" -> Recurly -> webhooks.io -> marketo-tools -> Marketo
+```
+
+TODO (rspeicher): Explain purpose.
+
+**Relevant issues:**
+
+- [Webhook to send code for free trial](https://gitlab.com/gitlab-com/www-gitlab-com/issues/423)
+
+### Newsletter
+
+```text
+GitLab.com Sign-Up -> System Hook -> marketo-tools -> Marketo
+```
+
+Receives the `user_create` system hook from GitLab.com and creates or updates a
+lead in Marketo.
 
 This replaces our internal [mailchimp-tools] project.
 
-## Relevant issues
+**Relevant issues:**
 
 - [Point webhook from Mailchimp to Marketo](https://gitlab.com/gitlab-com/www-gitlab-com/issues/427)
 - [Remove nl-importer.gitlap.com](https://dev.gitlab.org/cookbooks/chef-repo/issues/316)
   (internal)
 
-## Development
+### Recurly
 
-```sh
-bundle install
-bundle exec rackup -p 4567
-open http://localhost:4567/
+```text
+"Buy Now" -> Recurly -> webhooks.io -> marketo-tools -> Marketo
 ```
 
+Receives a Recurly hook (via webhooks.io splitter) and forwards information to
+Marketo.
+
+TODO (rspeicher): Expand on information forwarded.
+
+**Relevant issues:**
+
+- [Replace all Wufoo forms with Marketo forms](https://gitlab.com/gitlab-com/www-gitlab-com/issues/422)
+
+## Development
+
+1. Edit the `.env` file to view or change the HTTP Basic Auth credentials and to
+   add the Marketo API keys.
+1. Start the server:
+
+    ```sh
+    bundle install
+    bundle exec rackup -p 4567
+    ```
+
 ## Deployment
 
 This project stores HTTP Basic Auth credentials and Marketo API keys in the
-environment, using [Dotenv]. The default values should be overridden in a
-`.env.production` file.
+environment variables, using [Dotenv]. The default values should be overridden
+in a `.env.production` file for deployment.
 
 ## License