Added feedback form

mkdocs.yml

@@ -76,4 +76,6 @@ nav:
       - Double Slit Diffraction: simulations/double_slit_diffraction.md
       - N Slit Diffraction: simulations/n_slit_diffraction.md
   - Game:
-      - Game: text/game/main.md
+      - Game: text/game/main.md
+  - Feedback:
+      - Feedback: text/feedback/main.md

src/text/feedback/main.md

@@ -0,0 +1,5 @@
+**We hope that you have had fun in our website!**
+
+Please help us fill in the google form to provide us with feedbacks, so that we can constantly improve and make this site better for you!
+
+<iframe src="https://docs.google.com/forms/d/e/1FAIpQLSeSlfQ9KAR9vys3W9OmRXA8m_dh4chBl0l3p7gv9PswfpC-_Q/viewform?embedded=true" width="640" height="2396" frameborder="0" marginheight="0" marginwidth="0">Loading…</iframe>