add upgrading info

UPGRADING.md

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+# Upgrading Replicated Security
+
+This guide provides instructions for upgrading to specific versions of Replicated Security.
+
+## [v3.0.x](https://github.com/cosmos/interchain-security/releases/tag/v3.0.0-rc0)
+
+### Upgrading to Cosmos SDK 0.47
+
+The following should be considered as complementary to [Cosmos SDK v0.47 UPGRADING.md](https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc2/UPGRADING.md).
+
+#### Protobuf 
+
+Protobuf code generation, linting and formatting have been updated to leverage the `ghcr.io/cosmos/proto-builder:0.11.5` docker container. Replicated Security protobuf definitions are now packaged and published to [buf.build/cosmos/replicated-security](https://buf.build/cosmos/replicated-security) via CI workflows. The `third_party/proto` directory has been removed in favour of dependency management using [buf.build](https://docs.buf.build/introduction).
+
+#### App modules
+
+Legacy APIs of the `AppModule` interface have been removed from ccv modules. For example, for 
+
+```diff
+- // Route implements the AppModule interface
+- func (am AppModule) Route() sdk.Route {
+-     return sdk.Route{}
+- }
+-
+- // QuerierRoute implements the AppModule interface
+- func (AppModule) QuerierRoute() string {
+-     return types.QuerierRoute
+- }
+-
+- // LegacyQuerierHandler implements the AppModule interface
+- func (am AppModule) LegacyQuerierHandler(*codec.LegacyAmino) sdk.Querier {
+-     return nil
+- }
+-
+- // ProposalContents doesn't return any content functions for governance proposals.
+- func (AppModule) ProposalContents(_ module.SimulationState) []simtypes.WeightedProposalContent {
+-     return nil
+- }
+```
+
+#### Imports
+
+Imports for ics23 have been updated as the repository have been migrated from confio to cosmos.
+
+```diff
+import (
+    // ...
+-   ics23 "github.com/confio/ics23/go"
++   ics23 "github.com/cosmos/ics23/go"
+    // ...
+)
+```
+
+Imports for gogoproto have been updated.
+
+```diff
+import (
+    // ...
+-   "github.com/gogo/protobuf/proto"
++   "github.com/cosmos/gogoproto/proto"
+    // ...
+)
+```
+
+## [v2.0.x](https://github.com/cosmos/interchain-security/releases/tag/v2.0.0)
+
+### Provider 
+
+Upgrading a provider from `v1.1.0-multiden` to `v2.0.0` will require state migrations. See [migration.go](./x/ccv/provider/keeper/migration.go). See the provider module's `ConsensusVersion` in [module](./x/ccv/provider/module.go).
+
+### Consumer
+
+Upgrading a consumer from `v1.2.0-multiden` to `v2.0.0` will NOT require state migrations. See the consumer module's `ConsensusVersion` in [module](./x/ccv/consumer/module.go).