INSTALL.md: more workarounds for the insanity of Windows

Apparently trying to use a direct download link for the git-filter-repo
script results in Windows trying to give the file an unwanted extension.
Warn users about that stupidity.

While at it, also:
  * note in the pre-reqs section that we have later hints for Windows
    users about installing Python
  * provide an additional link for installing Python on Windows that
    isn't generic instructions about using Python on Windows but helps
    users find the latest python to install from the Microsoft store

Reported-by: Radu Terec <raduterec@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>

INSTALL.md

@@ -11,14 +11,17 @@
 # Pre-requisites
 
 Instructions on this page assume you have already installed both
-[Git](https://git-scm.com) and [Python](https://www.python.org/).
+[Git](https://git-scm.com) and [Python](https://www.python.org/)
+(though the [Notes for Windows Users](#notes-for-windows-users) has
+some tips on Python).
 
 # Simple Installation
 
-All you need to do is download the [git-filter-repo script in this
-repository](git-filter-repo) ([direct link to raw
-file](https://raw.githubusercontent.com/newren/git-filter-repo/main/git-filter-repo)).
-**That's it**.  You're done.
+All you need to do is download one file: the [git-filter-repo script
+in this repository](git-filter-repo) ([direct link to raw
+file](https://raw.githubusercontent.com/newren/git-filter-repo/main/git-filter-repo)),
+making sure to preserve its name (`git-filter-repo`, with no
+extension).  **That's it**.  You're done.
 
 Then you can run any command you want, such as
 
@@ -146,15 +149,17 @@ you'll still need to do that yourself.
 
 Windows likes to make things difficult.  Common and historical issues:
 
-  * [**Non-functional Python
-    stub**](https://github.com/newren/git-filter-repo/issues/36#issuecomment-568933825):
-    Windows apparently ships with a non-functional python.  This can
-    even manifest as [the app
+  * **Non-functional Python stub**: Windows apparently ships with a
+    [non-functional
+    python](https://github.com/newren/git-filter-repo/issues/36#issuecomment-568933825).
+    This can even manifest as [the app
     hanging](https://github.com/newren/git-filter-repo/issues/36) or
     [the system appearing to
     hang](https://github.com/newren/git-filter-repo/issues/312).  Try
-    installing Python from the [Microsoft
-    Store](https://docs.microsoft.com/en-us/windows/python/beginners)
+    installing
+    [Python](https://docs.microsoft.com/en-us/windows/python/beginners)
+    from the [Microsoft
+    Store](https://apps.microsoft.com/store/search?publisher=Python%20Software%20Foundation)
   * **Modifying PATH, making the script executable**: For some reason lots of
     Windows users have a hard time modifying their PATH and/or making scripts
     executable.  You can skip that step by just using