doc: avoid using the gender of other people

doc: avoid using the gender of other people

Using gendered pronouns for an anonymous person applies a gender where
none is known and further excludes readers who do not use gendered
pronouns. Avoid such examples in the documentation by using "they" or
passive voice to avoid the need for a pronoun.

Inspired-by: Derrick Stolee <redacted>
Signed-off-by: Felipe Contreras <redacted>
Signed-off-by: Derrick Stolee <redacted>
Signed-off-by: Junio C Hamano <redacted>