add metadata health coverage explanation

app.py

@@ -260,7 +260,14 @@ with gr.Blocks() as demo:
         library_choice.change(
             tag_frequency_by_library, [library_choice], df, queue=False
         )
-    with gr.Tab("Tag health by library"):
+    with gr.Tab("Metadata coverage by library"):
+        gr.Markdown(
+            "Libraries hosting models on the Hugging Face hub take different approaches to "
+            "metadata i.e. some libraries automatically generate metadata for a model at the end of a "
+            "training run. These libraries may also have different types of users who take differing "
+            "approaches to creating metadata for models they share on the hub. The below chart allows you to "
+            "see which libraries have better coverage for key areas of model metadata. "
+        )
         metadata_field = gr.Dropdown(choices=metadata_coverage_columns)
         plot = gr.Plot()
         metadata_field.change(