doc: git-add: simplify discussion of ignored files

- Mention the --force option earlier
- Remove the explanation of shell globbing vs git's internal glob
  system, it's a common gotcha but I don't think this is an appropriate
  place to explain that concept. There's some discussion of the gotchas
  around globbing and `git add` in the EXAMPLES section which I think
  is clearer.

Signed-off-by: Julia Evans <[email protected]>

Author: jvns

Documentation/git-add.adoc

@@ -34,12 +34,11 @@ you must run `git add` again to add the new content to the index.
 The `git status` command can be used to obtain a summary of which
 files have changes that are staged for the next commit.
 
-The `git add` command will not add ignored files by default.  If any
-ignored files were explicitly specified on the command line, `git add`
-will fail with a list of ignored files.  Ignored files reached by
-directory recursion or filename globbing performed by Git (quote your
-globs before the shell) will be silently ignored.  The `git add` command can
-be used to add ignored files with the `-f` (force) option.
+`git add` will not add ignored files by default. You can use the
+`--force` option to add ignored files. If you explicitly specify the
+exact filename of an ignored file (e.g. `git add ignored.txt`), `git
+add` will fail with a list of ignored files. Otherwise it will silently
+ignore the file.
 
 OPTIONS
 -------