Problem: non-stable Gravity Bridge module related functionality (#168)

Solution: drafted ADR to disable Gravity Bridge at genesis

docs/architecture/README.md

@@ -26,4 +26,5 @@ To suggest an ADR, please make use of the [ADR template](./adr-template.md) prov
 ## Table of Contents
 
 | ADR \# | Description | Status |
-| ------ | ----------- | ------ |
+| ------ | ----------- | ------ |
+| [001](./adr-001.md) | Disable Gravity Bridge at Genesis | Proposed |

docs/architecture/adr-001.md

@@ -0,0 +1,51 @@
+# ADR 001: Disable Gravity Bridge at Genesis
+
+## Changelog
+* 12-10-2021: Initial Draft
+* 13-10-2021: Code deletion instead of conditional compilation
+
+## Context
+
+The Gravity Bridge module was added for fungible asset transfers from and to the Ethereum network.
+Additionally, custom code was added for directly mapping the native tokens from Gravity Bridge
+to the Ethermint module. At the time of writing, Gravity Bridge does not have a stable release
+and the codebase contains several known issues.
+
+## Decision
+
+The Gravity Bridge module will be removed from:
+1. "app/app.go" which contains the module initialization boilerplate
+2. "cmd/cronosd/cmd/root.go" which adds Gravity Bridge-related commands.
+
+In addition to that, the "x/cronos" module contains Gravity Bridge-related code in its types and keeper. This following code will be removed:
+1. the whole x/cronos/keeper/gravity_hooks.go module
+2. the gravityKeeper field in CronosKeeper
+
+Existing integration tests related to Gravity Bridge can be temporarily disabled and later enabled when Gravity Bridge is added back.
+
+Once the Gravity Bridge code is added back, the x/cronos module `ConsensusVersion` should be increased and the corresponding upgrade handler should be added.
+
+## Status
+
+Accepted
+
+## Consequences
+
+### Positive
+* Reduced complexity in the initial Cronos state
+* Reduced complexity in the initial infrastructure deployment 
+* Possible to add the Gravity Bridge module in a coordinated upgrade when the module gets a stable release
+
+### Negative
+* Not testing Gravity Bridge temporarily
+
+### Neutral
+* A need for a breaking change upgrade
+
+## References
+
+* https://github.com/althea-net/cosmos-gravity-bridge/issues/348
+* https://github.com/althea-net/cosmos-gravity-bridge/issues/347
+* https://github.com/althea-net/cosmos-gravity-bridge/issues/346
+* https://github.com/althea-net/cosmos-gravity-bridge/issues/344
+* in-place store migrations: https://github.com/cosmos/cosmos-sdk/blob/a47bd592e951d34ebbffca03f85ca98d65b61be8/docs/architecture/adr-041-in-place-store-migrations.md