[plugin-server] Add PostHog local dev instructions (PostHog/plugin-se…

…rver#447)

README.md

@@ -11,7 +11,7 @@ Let's get you developing the plugin server in no time:
 
 1. Install dependencies and prepare for takeoff by running command `yarn`.
 
-1. Start a development instance of [PostHog](/PostHog/posthog). After all, this is the _PostHog_ Plugin Server, and it works in conjuction with the main server. To avoid interference, disable the plugin server there with setting the PLUGIN_SERVER_IDLE env variable before running. `PLUGIN_SERVER_IDLE=true ./bin/start`
+1. Start a development instance of [PostHog](/PostHog/posthog) - [instructions here](https://posthog.com/docs/developing-locally). After all, this is the _PostHog_ Plugin Server, and it works in conjuction with the main server. To avoid interference, disable the plugin server there with setting the PLUGIN_SERVER_IDLE env variable before running. `PLUGIN_SERVER_IDLE=true ./bin/start`
 
 1. Make sure that the plugin server is configured correctly (see [Configuration](#Configuration)). Two settings that you MUST get right are DATABASE_URL and REDIS_URL - they need to be identical between the plugin server and the main server.