bug#36644: Git log search

[Juri Linkov]

>> "Search a log of changes for PATTERN.
>>
>> How PATTERN is interpreted will depend on how each individual
>> backend's log search command is implemented, as some can only match
>> fixed strings, some have regular expression support, etc."
>
> I think this should also mention that most backends will interpret
> PATTERN as a regular expression.  Something like this:
>
>     "Search the log of changes for PATTERN.
>
>   PATTERN is usually interpreted as a regular expression.  However, its
>   exact semantics is up to the backend's log search command; some can
>   only match fixed strings."

So I fixed this accordingly.