Update CODEOWNERS (#237)

Author: dweindl

.github/CODEOWNERS

@@ -3,10 +3,10 @@
 # default owners
 * @PEtab-dev/libpetab-python-maintainers
 
-/petab/visualize/ @plakrisenko
-/tests/test_vis* @plakrisenko
+/petab/visualize/ @m-philipps
+/tests/test_vis* @m-philipps
 /petab/simulate.py @dilpath
 /tests/test_simulate.py @dilpath
-/petab/calculate.py @yannikschaelte
-/tests/test_calculate.py @yannikschaelte
 /doc/ @dweindl
+/doc/example @m-philipps
+/doc/example/example_petablint.ipynb @dweindl