git-worktree.txt: fix missing ")" typo

Add the closing ")" to a parenthetical phrase introduced by 4e85333197
(worktree: make add <path> <branch> dwim, 2017-11-26).

While at it, add a missing ":" at the end of the same sentence since
it precedes an example literal command block.

Reported-by: Mike Nordell <tamlin.thefirst@gmail.com>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-worktree.txt

@@ -52,10 +52,10 @@ is linked to the current repository, sharing everything except working
 directory specific files such as HEAD, index, etc. `-` may also be
 specified as `<commit-ish>`; it is synonymous with `@{-1}`.
 +
-If <commit-ish> is a branch name (call it `<branch>` and is not found,
+If <commit-ish> is a branch name (call it `<branch>`) and is not found,
 and neither `-b` nor `-B` nor `--detach` are used, but there does
 exist a tracking branch in exactly one remote (call it `<remote>`)
-with a matching name, treat as equivalent to
+with a matching name, treat as equivalent to:
 ------------
 $ git worktree add --track -b <branch> <path> <remote>/<branch>
 ------------