Added quirks section to migration guide

Documentation/SnapKit 3.0 Migration Guide.md

@@ -9,3 +9,8 @@ SnapKit 3.0 has many breaking changes from earlier versions. You can read the [n
 5. Test every screen of UI to ensure visual compatibility
 
 If you find any issues with migration please open an issue.
+
+### Known Quirks
+
+1. `make.center.equalTo(0)` now positions a view at 0,0 in it's superview rather than the center, use `make.center.equalToSuperview` instead.
+2. `updateConstraints` will throw a fatal error if it generates a *new* constraint that did not exist before. Instead use `makeConstraints` to add additional constraints.