docs: typo at controller.md

[lslxdx]

Checklist

• documentation is changed or added

Affected core subsystem(s)

Description of change

将“字符数”改为“字节数”。因为Content-Length表示的是”字节数“。原文中的“字符数”不是很精确。

[mention-bot]

@lslxdx, thanks for your PR! By analyzing the history of the files in this pull request, we identified @dead-horse, @huacnlee and @atian25 to be potential reviewers.

[popomore]

注意 commit message 要加 docs:

[atian25]

没关系了，我们把 PR title 改了， squash 的时候注意下就好了。

[codecov]

Codecov Report

Merging #720 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #720   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          26     26           
  Lines         640    637    -3     
=====================================
- Hits          640    637    -3

Impacted Files	Coverage Δ
index.js	100% <0%> (ø)	⬆️

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[lslxdx]

@popomore 好的 👍 。第一次提交所以有点紧张，下次会注意的。