Keyring migrate command doc (#8979) (#9254)

Co-authored-by: SaReN <sahithnarahari@gmail.com>
Co-authored-by: Barrie Byron <barrie.byron@tendermint.com>
Co-authored-by: Alessio Treglia <alessio@tendermint.com>
Co-authored-by: Amaury <1293565+amaurym@users.noreply.github.com>
(cherry picked from commit d5f5fe6)
Co-authored-by: Andrei Ivasko <cyberbono3@gmail.com>

docs/migrations/README.md

@@ -11,3 +11,4 @@ This folder contains all the migration guides to update your app and modules to
 1. [App and Modules Migration](./app_and_modules.md)
 1. [Chain Upgrade Guide to v0.40](./chain-upgrade-guide-040.md)
 1. [REST Endpoints Migration](./rest.md)
+1. [Keyring Migration](./keyring.md)

docs/migrations/keyring.md

@@ -0,0 +1,31 @@
+<!--
+order: 4
+-->
+# Keyring Migrate Quick Start
+
+`keyring` is the Cosmos SDK mechanism to manage the public/private keypair. Cosmos SDK v0.42 (Stargate) introduced breaking changes in the keyring. 
+
+To upgrade your chain from v0.39 (Launchpad) and earlier to Stargate, you must migrate your keys inside the keyring to the latest version. For details on configuring and using the keyring, see [Setting up the keyring](../run-node/keyring.md).
+
+This guide describes how to migrate your keyrings.
+
+The following command migrates your keyrings:
+
+```bash
+Usage
+simd keys migrate <old_home_dir>
+```
+
+The migration process moves key information from the legacy db-based Keybase to the [keyring](https://github.com/99designs/keyring)-based Keyring. The legacy Keybase persists keys in a LevelDB database in a 'keys' sub-directory of the client application home directory (`old_home_dir`). For example, `$HOME/.gaiacli/keys/` for [Gaia](https://github.com/cosmos/gaia).
+
+You can migrate or skip the migration for each key entry found in the specified  `old_home_dir` directory. Each key migration requires a valid passphrase. If an invalid passphrase is entered, the command exits. Run the command again to restart the keyring migration. 
+
+The `migrate` command takes the following flags:
+- `--dry-run` boolean
+
+     - true - run the migration but do not persist changes to the new Keybase. 
+     - false - run the migration and persist keys to the new Keybase. 
+
+Recommended: Use `--dry-run true` to test the migration without persisting changes before you migrate and persist keys. 
+
+- `--keyring-backend` string flag. It allows you to select a backend. For more detailed information about the available backends, you can read [the keyring guide](../run-node/keyring.md).