feat(proposal): add AWE1549 to background

pub/proposal/references.bib

@@ -0,0 +1,13 @@
+@report{AWE1549,
+  author          = {National Tranportation Safety Board},
+  number          = {PB2010-910403},
+  title           = {Loss of Thrust in Both Engines
+  After Encountering a Flock of Birds
+  and Subsequent Ditching on the Hudson River},
+  type            = {Technical Report},
+  institution     = {},
+  date            = {2010},
+  month           = {5},
+  day             = {3},
+  url             = {https://www.ntsb.gov/investigations/Pages/DCA09MA026.aspx},
+}