[PATCH v2] git-submodule.txt: fix AsciiDoc formatting error

In b57e8119e6 (submodule: teach set-branch subcommand, 2019-02-08), the `set-branch` subcommand was added for submodules. When the documentation was written, the syntax for a "index term" in AsciiDoc was accidentally used. This caused the documentation to be rendered as

	set-branch -d|--default)|(-b|--branch <branch> [--] <path>

instead of

	set-branch ((-d|--default)|(-b|--branch <branch>)) [--] <path>

In addition to this, the original documentation was possibly confusing as it made it seem as if the `-b` option didn't accept a `<branch>` argument.

Break `--default` and `--branch` into their own separate invocations to make it obvious that these options are mutually exclusive. Also, this removes the surrounding parentheses so that the "index term" syntax is not triggered.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
---

Thanks for reviewing, Junio.

I thought about it over the weekend and I hope that this is a good compromise.

I looked through other options in the documentation and I couldn't find any other places where a short-form was documented in the body instead of in the summary line so I didn't want to introduce that with this commit. I feel like it would be unfamiliar to someone who's used to reading other Git documentation.

Also, I opted to separate the the options onto their own lines because this makes it obvious that these two arguments are incompatible. Hopefully, this assuages your concerns.

Range-diff against v1:
1:  796a25ee1e ! 1:  2ae16375ba git-submodule.txt: fix AsciiDoc formatting error
    @@ Commit message
     
         instead of
     
    -            set-branch (-d|--default)|(-b|--branch <branch>) [--] <path>
    +            set-branch ((-d|--default)|(-b|--branch <branch>)) [--] <path>
     
    -    Remove surrounding parentheses so that the "index term" syntax is not
    -    triggered (and because it looks nicer without them anyway ;) ).
    +    In addition to this, the original documentation was possibly confusing
    +    as it made it seem as if the `-b` option didn't accept a `<branch>`
    +    argument.
    +
    +    Break `--default` and `--branch` into their own separate invocations to
    +    make it obvious that these options are mutually exclusive. Also, this
    +    removes the surrounding parentheses so that the "index term" syntax is
    +    not triggered.
     
         Signed-off-by: Denton Liu <liu.denton@gmail.com>
     
    @@ Documentation/git-submodule.txt: submodule with the `--init` option.
      registered submodules, and update any nested submodules within.
      --
     -set-branch ((-d|--default)|(-b|--branch <branch>)) [--] <path>::
    -+set-branch (-d|--default)|(-b|--branch <branch>) [--] <path>::
    ++set-branch (-b|--branch) <branch> [--] <path>::
    ++set-branch (-d|--default) [--] <path>::
      	Sets the default remote tracking branch for the submodule. The
      	`--branch` option allows the remote branch to be specified. The
      	`--default` option removes the submodule.<name>.branch configuration

 Documentation/git-submodule.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)