chore: README for n:upgrade-next

Author: mujahidkay

a3p-integration/proposals/n:upgrade-next/README.md

@@ -0,0 +1,14 @@
+# Proposal to upgrade the chain software
+
+The `UNRELEASED_A3P_INTEGRATION` software upgrade may include core proposals
+defined in its upgrade handler. See `CoreProposalSteps` in the
+`unreleasedUpgradeHandler` in
+[golang/cosmos/app/upgrade.go](../../../golang/cosmos/app/upgrade.go).
+
+This test proposal may also include `coreProposals` in its `upgradeInfo`, which
+are executed after those defined in that upgrade handler. See `agoricProposal`
+in [package.json](./package.json).
+
+The "binaries" property of `upgradeInfo` is now required since Cosmos SDK 0.46,
+however it cannot be computed for an unreleased upgrade. To disable the check,
+`releaseNotes` is set to `false`.