Updating the Readme.md with new env variables

README.md

@@ -172,6 +172,7 @@ The docker image `ghcr.io/afitzek/hasura-metric-adapter:v0.1.6` needs four envir
 `LISTEN_ADDR`: The listen address for the metric endpoint
 `LOG_FILE`: The log file, which will hold the hasura logs
 `HASURA_GRAPHQL_ENDPOINT` The hasura endpoint (defaults to `http://localhost:8080`)
+`OPENTEL_ENDPOINT` The Open Telemetry collector endpoint (defaults to `http://localhost:4317`)
 `HASURA_GRAPHQL_ADMIN_SECRET` The hasura admin secret this is required
 
 ## K8S Example