docs: add instructions for specifying --coin-type during key restoring

Many relayer operators have struggled with restoring accounts without
knowing how to set the --coin-type properly. To address this, added
guidance on specifying the --coin-type for successful key restoration.

Signed-off-by: Hwangjae Lee <meetrick@gmail.com>

README.md

@@ -112,6 +112,13 @@ Additional information on how IBC works can be found [here](https://ibc.cosmos.n
    $ rly keys restore cosmoshub [key-name] "mnemonic words here"
    $ rly keys restore osmosis [key-name] "mnemonic words here"
    ```
+   Some projects require specifying the `--coin-type` in decimal format for the key to be restored correctly.
+   Always ensure to verify the `--coin-type` when restoring an account.
+
+   For example, in the case of Injective, the `--coin-type` should be set to `60`.
+   ```shell
+   $ rly keys restore injective [key-name] "mnemonic words here" --coin-type 60
+   ```
 
 5. **Use the `key-name` created above.**