docs: .gitignore parsing is to the top of the repo

The current documentation reads as if .gitignore files will be parsed in
every parent directory, and not until they reach a repository boundary.
This clarifies the current behaviour.

As well, this corrects 'toplevel' to 'top-level', matching usage for
'top-level domain'.

Signed-off-by: Andrew Berry <andrew@furrypaws.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitignore.txt

@@ -27,12 +27,11 @@ precedence, the last matching pattern decides the outcome):
    them.
 
  * Patterns read from a `.gitignore` file in the same directory
-   as the path, or in any parent directory, with patterns in the
-   higher level files (up to the toplevel of the work tree) being overridden
-   by those in lower level files down to the directory containing the file.
-   These patterns match relative to the location of the
-   `.gitignore` file.  A project normally includes such
-   `.gitignore` files in its repository, containing patterns for
+   as the path, or in any parent directory (up to the top-level of the working
+   tree), with patterns in the higher level files being overridden by those in
+   lower level files down to the directory containing the file. These patterns
+   match relative to the location of the `.gitignore` file.  A project normally
+   includes such `.gitignore` files in its repository, containing patterns for
    files generated as part of the project build.
 
  * Patterns read from `$GIT_DIR/info/exclude`.