Improve burst size doc

[antifuchs]

This fixes #184. Thanks for the suggestion, @brprkr!

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (ac86b49) 97.52% compared to head (cf50c89) 97.52%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #185 +/- ## ======================================= Coverage 97.52% 97.52% ======================================= Files 31 31 Lines 2220 2220 ======================================= Hits 2165 2165 Misses 55 55 ``` | [Impacted Files](https://codecov.io/gh/antifuchs/governor/pull/185?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Fuchs) | Coverage Δ | | |---|---|---| | [governor/src/quota.rs](https://codecov.io/gh/antifuchs/governor/pull/185?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Fuchs#diff-Z292ZXJub3Ivc3JjL3F1b3RhLnJz) | `100.00% <ø> (ø)` | | 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=Andreas+Fuchs). 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=Andreas+Fuchs)

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[antifuchs]

bors merge

[bors[bot]]

Build succeeded:

• all_tests
• cargo_clippy
• cargo_deny
• rustfmt