Adds an example to the README

Author: chris-79

README.md

@@ -19,3 +19,48 @@ In your template, use the filter like this:
 ```
 
 If `tf_slug` is not provided, it defaults to the value of `{{ last_segment }}`.
+
+## Example
+
+Say you have a collection with the slug `events` and you want to filter them based on a related Taxonomy that has the slug `events-categories`.
+
+In each `event` entry, you would have an array with the same name as the Taxonomy's slug, `events-categories` like this:
+
+```
+events-categories:
+  - 820aea27-1925-44a0-8819-ac12f4a9e0a7
+  - 6594680e-3a94-4e54-a4ad-aa031995af66
+  - 0246bd34-ef66-4c4c-8191-98461b58a215
+```
+
+… where each of those IDs matches-up with IDs in the `events-categories` Taxonomy.
+
+In my use case, I'm trying to filter based on the URI `/events/categories/summer`, grabbing only (upcoming) events tagged as "summer".
+
+### Template
+
+```
+{{ collection:events filter="TaxonomyFilter"
+                     tf_group="events-categories"
+                     tf_slug="{ slug }"
+                     sort="date:asc"
+                     show_future="yes"
+                     show_past="no"
+                     as="events"
+}}
+  {{ unless no_results }}
+    <h2>
+      <small>Upcoming events tagged:</small><br>
+      {{ slug|deslugify }}
+    </h2>
+    {{ events }}
+      {{ partial:calendar/item }}
+    {{ /events }}
+  {{ else }}
+    <p>
+      It seems there are no upcoming events
+      in the category "<strong>{{ slug|deslugify }}</strong>"
+    </p>
+  {{ /unless }}
+{{ /collection:events }}
+```