DOC: Rewrite remove-silent-labels-textgrid.md, fix #244

[NickleDave]

• Rename/rewrite -> doc/howto/munging-annotations-textgrid.md
• Add 4 TextGrid files in doc/data/r6paq/

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.06 :warning:

Comparison is base (177df2e) 93.96% compared to head (e2710e7) 93.91%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #251 +/- ## ========================================== - Coverage 93.96% 93.91% -0.06% ========================================== Files 43 43 Lines 1658 1659 +1 ========================================== Hits 1558 1558 - Misses 100 101 +1 ``` [see 1 file with indirect coverage changes](https://codecov.io/gh/vocalpy/crowsetta/pull/251/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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