Update local dev instructions

Makefile

@@ -6,9 +6,9 @@ check-deps:
 
 # https://mosquitto.org/man/mosquitto-tls-7.html
 # FOR LOCAL DEV ONLY! These certs do not use encryption. Use let's encrypt or a real cert.
-gen-local-tls:
+gen-local-tls-certs:
 	./scripts/gen-local-tls-certs.sh
-.PHONEY: gen-local-tls
+.PHONEY: gen-local-tls-certs
 
 start-dev:
 	docker compose up -d

README.md

@@ -5,19 +5,28 @@ Learning MQTT with Golang by doing. This repo is a simple example of using a Gol
 
 ## Development
 
-For local development we use [Mosquitto](https://mosquitto.org/). Start the local development environment with:
+For local development we use [Mosquitto](https://mosquitto.org/) as our MQTT broker, with TLS enabled. 
+
+First generate local development certs using:
+
+```
+make gen-local-tls-certs
+```
+
+This will create CA, server, and client certificates suitable for local development. Server and CA certs are created in `./.mosquitto/certs`. The client cert is create in the project root. 
+
+Start the local development environment with:
 
 ```
 make start-dev
 ```
 
-Stop with
+Stop the local development environment with:
 
 ```
 make stop-dev
 ```
 
-
 ## Usage
 
 *Instructions TBD*