fix mistakenly renamed development card id in the readme

Author: dbuezas

readme.md

@@ -759,7 +759,7 @@ refresh_interval: 5 # update every 5 seconds
 - run `npm i`
 - run `npm start`
 - From a dashboard in edit mode, go to `Manage resources` and add `http://127.0.0.1:8000/plotly-graph-card.js` as url with resource type JavaScript
-- ATTENTION: The development card is `type: custom:plotly-graph`
+- ATTENTION: The development card is `type: custom:plotly-graph-dev` (mind the extra `-dev`)
 - Either use Safari or Enable [chrome://flags/#unsafely-treat-insecure-origin-as-secure](chrome://flags/#unsafely-treat-insecure-origin-as-secure) and add your HA address (e.g http://homeassistant.local:8123): Chrome doesn't allow public network resources from requesting private-network resources - unless the public-network resource is secure (HTTPS) and the private-network resource provides appropriate (yet-undefined) CORS headers. More [here](https://stackoverflow.com/questions/66534759/chrome-cors-error-on-request-to-localhost-dev-server-from-remote-site)
 
 # Build