Use abosulute image links following Grafana's plugin guidelines

README.md

@@ -3,7 +3,7 @@
 # Traceroute Map Panel
 Traceroute Map Panel is a Grafana panel that visualize the traceroute hops in a map, just like [Besttrace](https://www.ipip.net/product/client.html).
 
-![Screenshot](./screenshot.png)
+![Screenshot](https://raw.githubusercontent.com/Gowee/traceroute-map-panel/master/screenshot.png)
 
 ## Data
 Currently, Traceroute Map Panel is only expected to work with traceroute data collected from [MTR](https://github.com/traviscross/mtr/) via [Telegraf](https://github.com/influxdata/telegraf) and stored in [InfluxDB](https://github.com/influxdata/influxdb).
@@ -57,4 +57,4 @@ If there is dynamic routing (e.g. multiple route paths for one src-dest pair), t
 In the current implementation, the Geo IP resolving is sequential, instead of concurrent. So it is predicatable that the map keeps loading for a long while at the first time. The resolving result is then cached in sessionStorage.
 
 ### Error processing data
-If it errors with "Error processing data", the problem could be failures in Geo IP resolving or invalid query data (response data is empty or the data is not [*Formatted as Table*](#query-in-grafana)). The detailed error is logged in the [debugging console](https://developer.mozilla.org/en-US/docs/Web/API/Console).
+If it errors with "Error processing data", the problem could be failures in Geo IP resolving or invalid query data (response data is empty or the data is not [*Formatted as Table*](#query-in-grafana)). The detailed error is logged in the [debugging console](https://developer.mozilla.org/en-US/docs/Web/API/Console).