Add documentation for GST_VALIDATE_PLUGIN_PATH

Add documentation for the environment variable, explaining what it is
used for and the default search locations.

Fixes: 83d6978f80 Implement fault_injection as a Gs(tValidate)Plugin
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1743>

diff --git a/subprojects/gst-devtools/docs/gst-validate-environment-variables.md b/subprojects/gst-devtools/docs/gst-validate-environment-variables.md
index 6cf48f9..42de2bf 100644 (file)
--- a/subprojects/gst-devtools/docs/gst-validate-environment-variables.md
+++ b/subprojects/gst-devtools/docs/gst-validate-environment-variables.md
@@ -35,6 +35,16 @@ outputed into the standard error.
 
 You can use the special names `stdout` and `stderr` to use those output.
 
+**GST_VALIDATE_PLUGIN_PATH.**
+
+Set this variable to a colon-separated list of paths. GstValidate will
+scan these paths for GstPlugin files and add them to the GstRegistry.
+By default GstValidate will look for plugins in the user data directory
+specified in the [XDG standard]:
+`.local/share/gstreamer-GST_API_VERSION/plugins` and the
+system wide user data directory:
+`/usr/lib/gstreamer-GST_API_VERSION/validate`
+
 **GST_VALIDATE_SCENARIOS_PATH.**
 
 Set this variable to a colon-separated list of paths. GstValidate will