docs: add update for min-gas-prices in local-testnet tutorial (backport

#1970) (#1971)

Co-authored-by: Kyle Lawlor-Bagcal <wgwz@users.noreply.github.com>

docs/ledger/get-started/local-testnet.md

@@ -96,6 +96,15 @@ regen collect-gentxs
 
 Now that you have updated the `genesis.json` file, you are ready to start the node. Starting a node with a new genesis file will create a new blockchain.
 
+## Set the minimum gas price
+
+We need to update the minimum gas price before we can start the node.
+Open the `~/.regen/config/app.toml` file and set the value as:
+
+```
+minimum-gas-prices = "0uregen"
+```
+
 ## Start Node
 
 Well, what are you waiting for?