Documentation: clarify .gitattributes search

Use the term "toplevel of the work tree" in gitattributes.txt and
gitignore.txt to define the limits of the search for those files.

Signed-off-by: Jason Merrill <jason@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -59,9 +59,9 @@ attribute.
 When deciding what attributes are assigned to a path, git
 consults `$GIT_DIR/info/attributes` file (which has the highest
 precedence), `.gitattributes` file in the same directory as the
-path in question, and its parent directories (the further the
-directory that contains `.gitattributes` is from the path in
-question, the lower its precedence).
+path in question, and its parent directories up to the toplevel of the
+work tree (the further the directory that contains `.gitattributes`
+is from the path in question, the lower its precedence).
 
 If you wish to affect only a single repository (i.e., to assign
 attributes to files that are particular to one user's workflow), then

Documentation/gitignore.txt

@@ -31,8 +31,8 @@ precedence, the last matching pattern decides the outcome):
 
  * 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 root) being overridden by those in
-   lower level files down to the directory containing the file.
+   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