CONTRIBUTING.md: fix typo

Signed-off-by: Wei Liu <liuw@liuw.name>
CONTRIBUTING.md: rephrase a sentence

Signed-off-by: Wei Liu <liuw@liuw.name>
humans.txt: remove Menglong Tan from maintainer list

He once submitted a PR to do so but it was not merged because the PR was
not clean.

See https://github.com/pythoncn/june/pull/69.

Signed-off-by: Wei Liu <liuw@liuw.name>
Cc: Menglong Tan <tanmenglong@gmail.com>
humans.txt: fix typo

Signed-off-by: Wei Liu <liuw@liuw.name>
Merge pull request #77 from liuw/doc-update

These are rather straight forward changes so I will just push them without an ACK.