update CONTRIBUTING with details on release process (#180)

* docs: update CONTRIBUTING with details on release process

CONTRIBUTING.md

@@ -2,8 +2,21 @@
 
 Each proposal to Mainnet (agoric-3) should be contributed to this repo before being proposed to the chain.
 
-1. Prepare the proposal and verify it running locally
+1. Prepare the proposal and verify it by creating a proposal in
+   agoric-sdk/a3p-integration. See the
+   [README](https://github.com/Agoric/agoric-sdk/blob/master/a3p-integration/README.md) for more details
+
 2. Submit a PR to this repo in which the proposal has a _pending_ name (e.g. `a:my-contract`)
+
 3. Get review and merge to main
+
 4. When the proposal has been further qualified with higher fidelity to Mainnet, submit to Mainnet
-5. When the proposal passes, submit a PR here converting the pending proposal to a passed one (by changing the letter to the submission number)
+
+5. When the proposal passes, submit a PR here converting the pending proposal to a passed one (by
+   changing the letter to the submission number)
+
+6. clean up a3p-integration
+  a. Move generally useful tools to the `@agoric/synthetic-chain` package.
+  b. Move tests that should continue to pass afterwards into a3p-integration/z:acceptance
+  c. Remove the proposal from a3p-integration.
+