word cloud: add more docs about `display_student_percents` options

doc/public/course_data_formats/word_cloud/word_cloud.rst

@@ -18,12 +18,17 @@ The following attributes can be specified for this tag::
     [display_name| AUTOGENERATE] – Display name of xmodule. When this attribute is not defined - display name autogenerate with some hash.
     [num_inputs| 5] – Number of inputs.
     [num_top_words| 250] – Number of max words, which will be displayed.
-    [display_student_percents| True] – Display usage percents for each word.
+    [display_student_percents| True] – Display usage percents for each word on the same line together with words.
+
+.. note::
+
+   Percent is shown always when mouse over the word in cloud.
 
 .. note::
 
    If you want to use the same word cloud (the same storage of words), you must use the same display_name value.
 
+
 Code Example
 ============