Documentation: user-manual: limit usage of ellipsis

Documentation: user-manual: limit usage of ellipsis

There is no need to use full 40-hex to identify the object names like
the examples hint at by omitting the tail part of an object name as if
that has to be spelled out but the example omits them only for brevity.
Give examples using abbreviated object names without ellipses just like
how people do in real life.

Signed-off-by: Ann T Ropea <redacted>
Signed-off-by: Junio C Hamano <redacted>