Update list of files that should not be ignored in .gitignore

.gitignore
- Create a new section of files that should not be ignored at the
  end of the file
- Explicitly request that docs/figures/*.pdf not be ignored
- Explicity request that util/{*.c, *.f, *.f90, *.h, *,m} and u
  util/Makefile* files should not be ignored
- Now ignore __pycache__ folders everywhere

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

Author: yantosca

.gitignore

@@ -6,7 +6,6 @@
 
 # Keep empty directory for executables, but ignore its contents
 /bin/*
-!/bin/.gitkeep
 
 # Ignore temporary files everywhere
 **/*.~*
@@ -60,5 +59,14 @@ docs/build/*
 
 # Ignore other files & folders
 *.pdf
-/examples/mcm*/__pycache__
+**/__pycache__
 
+# IMPORTANT: Do not ignore these files!
+!/bin/.gitkeep
+!/docs/figures/*.pdf
+!/util/*.c
+!/util/*.f
+!/util/*.h
+!/util/*.f90
+!/util/*.m
+!/util/Makefile*