add swiftformat config file

motivation: help contributors follow formatting conventions

changes: add swiftformat file that can be used before submitting PR

Author: tomerd

.swiftformat

@@ -0,0 +1,13 @@
+# file options
+
+--swiftversion 5.0
+--exclude .build
+
+# format options
+
+--self insert
+--patternlet inline
+--stripunusedargs unnamed-only
+--ifdef no-indent
+
+# rules