docs: filesystems: Add mount map description in Content

The second paragraph of the content section does not properly
describe how mount points are determined by autofs.

Replace the lines detailing how the determination of these mount
points is "ad hoc" by a short description of the mount map syntax
used by autofs.
Signed-off-by: Jaskaran Singh <jaskaransingh7654321@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/autofs.rst

@@ -49,9 +49,10 @@ extra properties as described in the next section.
 Objects can only be created by the automount daemon: symlinks are
 created with a regular `symlink` system call, while directories and
 mount traps are created with `mkdir`.  The determination of whether a
-directory should be a mount trap or not is quite ad hoc, largely for
-historical reasons, and is determined in part by the
-*direct*/*indirect*/*offset* mount options, and the *maxproto* mount option.
+directory should be a mount trap is based on a master map. This master
+map is consulted by autofs to determine which directories are mount
+points. Mount points can be *direct*/*indirect*/*offset*.
+On most systems, the default master map is located at */etc/auto.master*.
 
 If neither the *direct* or *offset* mount options are given (so the
 mount is considered to be *indirect*), then the root directory is