freezing: convergence analysis notebook update; adding typical output file extensions to .gitignore (#1137)

Author: slayoo

.gitignore

@@ -1,4 +1,9 @@
 PySDM_examples/utils/temporary_files/*
+*.pdf
+*.nc
+*.pkl
+*.vtu
+*.vts
 
 # Byte-compiled / optimized / DLL files
 __pycache__/
@@ -137,4 +142,4 @@ dmypy.json
 **.DS_Store
 
 #Jetbrains
-.idea/
+.idea/