docs: improve description of options behavior

[Midnighter]

• [x] fix #93
• [x] description of feature/fix
• [x] tests added/passed
• [x] add an entry to the changelog

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (e5f47f9) 81.64% compared to head (fd29c12) 81.64%.

:exclamation: Current head fd29c12 differs from pull request most recent head 478bf72. Consider uploading reports for the commit 478bf72 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #96 +/- ## ======================================== Coverage 81.64% 81.64% ======================================== Files 103 103 Lines 1585 1585 Branches 129 274 +145 ======================================== Hits 1294 1294 Misses 250 250 Partials 41 41 ``` | [Impacted Files](https://codecov.io/gh/taxprofiler/taxpasta/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [src/taxpasta/infrastructure/cli/merge.py](https://codecov.io/gh/taxprofiler/taxpasta/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL3RheHBhc3RhL2luZnJhc3RydWN0dXJlL2NsaS9tZXJnZS5weQ==) | `54.81% <ø> (ø)` | | | [src/taxpasta/infrastructure/cli/standardise.py](https://codecov.io/gh/taxprofiler/taxpasta/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL3RheHBhc3RhL2luZnJhc3RydWN0dXJlL2NsaS9zdGFuZGFyZGlzZS5weQ==) | `34.83% <ø> (ø)` | |

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