good first issue: add documentation for 3 undocumented public methods

In Spoon, we want that all public methods are properly documented.

We have a test case to check this: https://github.com/INRIA/spoon/blob/51c4b2211922e71914f74ce4341a6232c079f174/src/test/java/spoon/test/architecture/SpoonArchitectureEnforcerTest.java#L120

This test case temporarily skips small methods.

To get this issue done:

• List the undocumented public methods:
  • lower the threshold size() > 33 in the test case
  • run the test case, this will list you undocumented public methods
• Add appropriate Javadoc documentation /** .... */
• Create a pull request with your changes