Add a quick check for MST Store Python install (#5470)

Quick fix for #5467.

Checks if the path for python is under the windows store folder then
error and point the user to the beets
[documentation](https://beets.readthedocs.io/en/stable/guides/main.html).

Happy for feedback to improve, but thought it best to exit as early as
possible.

beets/ui/__init__.py

@@ -1858,6 +1858,14 @@ def main(args=None):
     """Run the main command-line interface for beets. Includes top-level
     exception handlers that print friendly error messages.
     """
+    if "AppData\\Local\\Microsoft\\WindowsApps" in sys.exec_prefix:
+        log.error(
+            "error: beets is unable to use the Microsoft Store version of "
+            "Python. Please install Python from https://python.org.\n"
+            "error: More details can be found here "
+            "https://beets.readthedocs.io/en/stable/guides/main.html"
+        )
+        sys.exit(1)
     try:
         _raw_main(args)
     except UserError as exc:

docs/changelog.rst

@@ -13,6 +13,11 @@ New features:
   many different artists at once.
 
 Bug fixes:
+
+* Check if running python from the Microsoft Store and provide feedback to install
+  from python.org.
+  :bug:`5467`
+
 For packagers:
 
 Other changes:

docs/guides/main.rst

@@ -109,7 +109,7 @@ get it right:
    should open the "System Properties" screen, then select the "Advanced" tab, 
    then hit the "Environmental Variables..." button, and then look for the PATH 
    variable in the table. Add the following to the end of the variable's value: 
-   ``;C:\Python37;C:\Python37\Scripts``. You may need to adjust these paths to 
+   ``;C:\Python38;C:\Python38\Scripts``. You may need to adjust these paths to 
    point to your Python installation.
 
 3. Now install beets by running: ``pip install beets``