Add flat bread trouble shooting

Debugging flat bread and how to fix it.

book/references.bib

@@ -14,4 +14,22 @@
   howpublished = {\url{https://www.youtube.com/watch?v=BUtn4HKAiBs}},
   year         = {2021},
   note         = {Accessed: 2022-03-24}
+}
+
+@article{rye-defects,
+ author    = {Marie Oest et al.},
+ title     = {Rye Bread Defects: Analysis of Composition and
+              Further Influence Factors as Determinants
+              of Dry-Baking},
+ journal   = {Applied and environmental microbiology},
+ publisher = {Foods},
+ url       = {https://www.mdpi.com/2304-8158/9/12/1900/pdf}
+}
+
+@article{stiff+starter,
+  title        = {Stiff sourdough starter},
+  author       = {Hendrik Kleinwächter},
+  howpublished = {\url{https://www.youtube.com/watch?v=MqH3GVfjfBc}},
+  year         = {2021},
+  note         = {Accessed: 2022-04-26}
 }