Docs: Fix link to roadmap (airbytehq#15103)

Replace the broken markdown link and add an external link to the roadmap.

Author: nialloriordan

README.md

@@ -62,7 +62,7 @@ For general help using Airbyte, please refer to the official Airbyte documentati
 
 ## Roadmap
 
-Check out our [roadmap](docs/project-overview/roadmap.md) to get informed on what we are currently working on, and what we have in mind for the next weeks, months and years.
+Check out our [roadmap](https://app.harvestr.io/roadmap/view/pQU6gdCyc/launch-week-roadmap) to get informed on what we are currently working on, and what we have in mind for the next weeks, months and years.
 
 ## License