add tutorial on working with large datasets

docs/guide/bigdata.md

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+# Working with Big Datasets
+
+When your `options` array gets into the thousands, you will start to see performance dip. If you 
+have 2,000 options, you have 2,000 dom nodes being rendered into the dropdown. It's very difficult
+to render that many nodes at once and maintain 60fps in the browser. 
+
+Regardless of whether your options are primitives or objects, the performance hit comes from 
+rendering their text labels (or slot) to the dom. The path to keeping things snappy is then to limit
+the amount of nodes that get rendered to the dropdown. 
+
+## Optimized Filtering
+
+You can optimize performance by tweaking Vue Select's filtering and implementing it yourself. 
+Consider a list of airport codes with roughly ~7,500 entries. Rendering out 7,500 airports doesn't 
+actually help the user much, they're just looking for one in particular.
+
+<AirportCodes />
+
+The only difference between these two examples is the `filter` prop. Here's the `filter` for the
+optimized example:
+
+```js
+filter (airports, search) {
+  if (search.length === 0) {
+    return airports.slice(0, 50);
+  }
+  return airports.filter(airport => {
+    const keys = ['name', 'city', 'country', 'iata', 'icao'];
+    return keys.some(key => String(airport[key]).toLowerCase().includes(search.toLowerCase()))
+  }).slice(0, 50);
+}
+```  
+
+If there's no search text, we only display the first 50 options. If there is a search query, we'll
+check if any keys on the object include the search string. Again, we'll limit this to 50 options. 
+
+The key to have Vue Select perform well with thousands of options is to limit the number of options
+that are displayed to the end user, without hindering their ability to select the right option.