docs: add jq doc for editing genesis file (cosmos#9918)

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## Description

Closes: cosmos#9908 

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docs/run-node/run-node.md

@@ -39,6 +39,24 @@ The `~/.simapp` folder has the following structure:
       |- priv_validator_key.json    # Private key to use as a validator in the consensus protocol.
 ```
 
+## Updating Some Default Settings
+
+If you want to change any field values in configuration files (for ex: genesis.json) you can use `jq` ([installation](https://stedolan.github.io/jq/download/) & [docs](https://stedolan.github.io/jq/manual/#Assignment)) & `sed` commands to do that. Few examples are listed here.
+```bash
+# to change the chain-id
+jq '.chain_id = "testing"' genesis.json > temp.json && mv temp.json genesis.json
+
+# to enable the api server
+sed -i '/\[api\]/,+3 s/enable = false/enable = true/' app.toml
+
+# to change the voting_period
+jq '.app_state.gov.voting_params.voting_period = "600s"' genesis.json > temp.json && mv temp.json genesis.json
+
+# to change the inflation
+jq '.app_state.mint.minter.inflation = "0.300000000000000000"' genesis.json > temp.json && mv temp.json genesis.json
+```
+
+## Adding Genesis Accounts
 Before starting the chain, you need to populate the state with at least one account. To do so, first [create a new account in the keyring](./keyring.md#adding-keys-to-the-keyring) named `my_validator` under the `test` keyring backend (feel free to choose another name and another backend).
 
 Now that you have created a local account, go ahead and grant it some `stake` tokens in your chain's genesis file. Doing so will also make sure your chain is aware of this account's existence: