Add thresholding slide

src/index.html

@@ -151,6 +151,22 @@
             - Image is just pixels (RGB)
           </aside>
         </section>
+        <section>
+          <h2 class="r-fit-text">2. Thresholding</h2>
+          <p class="fragment">Demo 🤞</p>
+          <aside class="notes" data-markdown>
+            - Images aren't black and white
+              - This slide is
+            - Markers _are_
+            - Discard the colour so the data we're working with is easier
+            - Grey is still more than enough data
+            - Black and white!
+            - Thresholding
+              - Naive thresholding based on a value
+              - Adaptive thresholding looks for hotspots and edges
+                - Useful in future
+          </aside>
+        </section>
       </div>
     </div>
     <script type="module" src="./index.js"></script>