Enhance README Clarity: Add Input/Output Type Information

## motivation
To enhance the clarity and usability of the READMEs in the assignment repositories, I propose adding clear information about the input and output types of the functions and classes used. This is especially important for the following reasons:

* **Cython Compatibility**: Some future assignments may utilize Cython, which requires explicit type declarations for optimal performance.
* **Type Hints in Python**: Even in pure Python code, type hints can improve code readability, maintainability, and help catch errors early on.
* **Clear Documentation**: Explicitly stating the expected input/output types makes it easier for users to understand and correctly utilize the provided code.

## assignments
* [ ] [wk02](https://github.com/kangwonlee/eca24-wk02-assignment)
* [ ] [wk03](https://github.com/kangwonlee/eca24-wk03-assignment)
* [x] [wk04](https://github.com/kangwonlee/eca24-wk04-assignment) https://github.com/kangwonlee/eca24-wk04-assignment/commit/76ef68340e6c5147ff43db6d3d16f998c8e1ab79
* [x] [wk05](https://github.com/kangwonlee/eca24-wk05-assignment) https://github.com/kangwonlee/eca24-wk05-assignment/commit/f3809756bd4c60a98fc0cee58aa4a23f376d8ab6
* [ ] [wk06](https://github.com/kangwonlee/eca24-wk06-assignment)
* [ ] [wk08](https://github.com/kangwonlee/eca24-wk08-assignment)
* [ ] [wk07](https://github.com/kangwonlee/eca24-wk07-assignment)
* [x] [wk10](https://github.com/kangwonlee/eca24-wk10-assignment) https://github.com/kangwonlee/eca24-wk10-assignment/commit/98cb33cf1dbb2c32554d30eef845592bd50a2994
* [x] [wk10 v 1](https://github.com/kangwonlee/eca24-wk10-012-assignment) https://github.com/kangwonlee/eca24-wk10-012-assignment/commit/bfb09d06223b1405356c4764102759f76af0b851
* [x] [wk10 v 2](https://github.com/kangwonlee/num_int_gaussian) https://github.com/kangwonlee/num_int_gaussian/commit/73467e5608a560416ab83d46e81b30ec8558ee54
* [x] [wk10 v 3](https://github.com/kangwonlee/cantilever_sfd_bmd) https://github.com/kangwonlee/cantilever_sfd_bmd/commit/b4b16f7016fc3c9ded3678e136eb40e653a64bff
* [x] [wk10 v 4](https://github.com/kangwonlee/beam_section) https://github.com/kangwonlee/beam_section/commit/b3d7f3c6c8493065821c8b5cd775a749b131c440
* [x] [wk12](https://github.com/kangwonlee/water_tank) https://github.com/kangwonlee/water_tank/commit/9f5dd038d019d29e4a739dacfd3e3d5aabcb0e84
* [x] [wk last](https://github.com/kangwonlee/damped_vibrations) https://github.com/kangwonlee/damped_vibrations/commit/1917b1a08fee6391ab6345d30198afbcf6866cf9

## acknowledge
* Thanks to @lucassuryana for the valuable feedback on this issue!
* Also I got help from an LLM to clarify & enhance the text here