Added postface and moved references there

teach_online/_toc.yml

@@ -8,3 +8,4 @@ chapters:
 - file: modalities
 - file: spicy
 - file: acknowledgements
+- file: postface

teach_online/acknowledgements.md

@@ -27,7 +27,3 @@ This online training module was developed with the support of a
 awarded to me (PI) and Karen Flammer (co-PI) by the
 [University of California Office of the President (UCOP)](https://www.ucop.edu/):
 *An Online Training Module to Provide Instructors Guidance in Developing and Offering Fully Online and Hybrid Courses*.
-
-```{bibliography}
-:style: unsrt
-```

teach_online/postface.md

@@ -0,0 +1,15 @@
+# Postface
+
+```{note}
+Source Code: [`teach_online/postface.md`](https://github.com/niemasd/How-to-Teach-Online/blob/main/teach_online/postface.md)
+```
+
+Thank you again for reading *How to Teach Online*!
+I sincerely hope you gained some useful information that you can incorporate into your own teaching,
+and if you think of anything you want to contribute,
+please feel free to create a [Pull Request](https://github.com/niemasd/How-to-Teach-Online/pulls)
+on [GitHub](https://github.com/niemasd/How-to-Teach-Online)!
+
+```{bibliography}
+:style: unsrt
+```