doc: fix the xunit-viewer installation command

README.md

@@ -85,7 +85,7 @@ To run the tests a running emulator or a connected device is required. There's a
 Test results can be viewed with any JUnit compatible viewer. For example, you can use `xunit-viewer` to view the results:
 
 ```bash
-pip install xunit-viewer
+npm i -g xunit-viewer
 xunit-viewer -r output.junit.xml
 ```