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

Start with src/test/java/spoon/test/architecture/SpoonArchitectureEnforcerTest.java and lower the size() > 33 threshold as described. Run the test to list the undocumented public methods, then add appropriate Javadoc comments to those methods. Done means the architecture test passes with the three methods documented and the changes are submitted in a pull request.

Written by the indexing model from the issue text.