validate README: Document paths for gst-examples

As the webrtc demos have now been merged, change the paths for
easier copy-pasting.

Part-of: <gstreamer/gst-examples!38>

webrtc/check/validate/README.md

@@ -14,4 +14,4 @@ testing framework.
 
 # Run the tests
 
-`GST_VALIDATE_APPS_DIR=/path/to/gstwebrtc-demos/check/validate/apps/ GST_VALIDATE_SCENARIOS_PATH=/path/to/gstwebrtc-demos/check/validate/scenarios/ gst-validate-launcher --testsuites-dir /path/to/gstwebrtc-demos/check/validate/testsuites/ webrtc`
+`GST_VALIDATE_APPS_DIR=/path/to/gst-examples/webrtc/check/validate/apps/ GST_VALIDATE_SCENARIOS_PATH=/path/to/gst-examples/webrtc/check/validate/scenarios/ gst-validate-launcher --testsuites-dir /path/to/gst-examples/webrtc/check/validate/testsuites/ webrtc`