DOCS/man/mpv: clarify config-dir path behavior

The previous documentation was pretty scary and misleading, and was also outdated in several sections.

It was also difficult to understand some of the paragraphs.

The path documentation has now been overhauled to be easier to understand and to document the latest mpv behavior.

DOCS/man/mpv.rst

@@ -499,32 +499,53 @@ console controls. (Which makes it suitable for playing data piped to stdin.)
 The special argument ``--`` can be used to stop mpv from interpreting the
 following arguments as options.
 
-When using the client API, you should strictly avoid using ``mpv_command_string``
+For paths passed to mpv CLI options, the situation is further complicated by the
+need to escape special characters. To work around this, the path can instead be
+wrapped in the "fixed-length" syntax, e.g. ``%n%string_of_length_n`` (see above).
+
+When using the libmpv API, you should strictly avoid using ``mpv_command_string``
 for invoking the ``loadfile`` command, and instead prefer e.g. ``mpv_command``
 to avoid the need for filename escaping.
 
-For paths passed to suboptions, the situation is further complicated by the
-need to escape special characters. To work this around, the path can be
-additionally wrapped in the fixed-length syntax, e.g. ``%n%string_of_length_n``
-(see above).
+The same applies when you're using the scripting API, where you should avoid using
+``mp.command``, and instead prefer using the "separate parameters" variants (such
+as ``mp.commandv`` or ``mp.command_native``), so that the filenames will always be
+correctly interpreted.
+
+Some mpv options will interpret special meanings for paths starting with ``~``,
+making it easy to dynamically find special directories, such as referring to the
+current user's home directory or the mpv configuration directory.
+
+When using the special ``~`` prefix, there must always be a trailing ``/`` after
+the special path prefix. In other words, ``~`` doesn't work, but ``~/`` will work.
+
+The following special paths/keywords are currently recognized:
+
+.. warning::
+
+    Beware that if ``--no-config`` is used, all of the "config directory"-based
+    paths (``~~/``, ``~~home/`` and ``~~global/``) will resolve to empty strings.
+
+    This means that commands such as ``expand-path "~~home/"`` will return an
+    empty string, and ``expand-path "~~home/foo/bar"`` will only return ``foo/bar``
+    (without any path prefix), which might not be what you expected.
+
+    Furthermore, certain commands such as ``mp.find_config_file("mpv.conf")``
+    won't have any config paths to search in, and would always return ``nil``,
+    which means "not found".
 
-Some mpv options interpret paths starting with ``~``.
-Currently, the prefix ``~~home/`` expands to the mpv configuration directory
-(usually ``~/.config/mpv/``).
-``~/`` expands to the user's home directory. (The trailing ``/`` is always
-required.) The following paths are currently recognized:
+    Be sure that your scripts can handle the "no config" scenarios.
 
 ================ ===============================================================
 Name             Meaning
 ================ ===============================================================
-``~~/``          If the subpath exists in any of the mpv's config directories
+``~~/``          If the subpath exists in any of mpv's config directories, then
                  the path of the existing file/dir is returned. Otherwise this
                  is equivalent to ``~~home/``.
-                 Note that if --no-config is used ``~~/foobar`` will resolve to
-                 ``foobar`` which can be unexpected.
-``~/``           user home directory root (similar to shell, ``$HOME``)
+``~/``           user home directory root (similar to a shell's ``$HOME``)
 ``~~home/``      mpv config dir (for example ``~/.config/mpv/``)
-``~~global/``    the global config path, if available (not on win32)
+``~~global/``    the global config path (such as ``/etc/mpv``), if available
+                 (not on win32)
 ``~~osxbundle/`` the macOS bundle resource path (macOS only)
 ``~~desktop/``   the path to the desktop (win32, macOS)
 ``~~exe_dir/``   win32 only: the path to the directory containing the exe (for