Add more documentation on merging res1d files

[ryan-kipawa]

It's currently possible to merge different kinds of res1d files, but the documentation is a bit light. So the proposal is to:

• Add a notebook example that covers merging and modifying res1d files
• Update documentation with similar example and explaining any limitations/preconditions

Relevant existing documentation:

mikeio1d/mikeio1d/res1d.py

Line 472 in 5070e29

def merge(file_names: List[str] | List[Res1D], merged_file_name: str):

mikeio1d/tests/test_res1d_lts_chronological.py

Line 258 in 5070e29

def test_res1d_merging_same_file(test_file_path):

mikeio1d/tests/test_res1d_lts_events.py

Line 223 in 5070e29

def test_res1d_merging_same_file(test_file_path):

mikeio1d/tests/test_res1d_catchments.py

Line 233 in 5070e29

def test_res1d_merging(test_file_path_for_merging):