Clarify that not-explicitly-supported platforms are unsupported

Co-authored-by: Paul Moore <[email protected]>
Co-authored-by: Xavier Fernandez <[email protected]>

docs/html/installation.md

@@ -81,8 +81,9 @@ pip is tested to work on the latest patch version of the Python interpreter,
 for each of the minor versions listed above. Previous patch versions are
 supported on a best effort approach.
 
-pip's maintainers do not provide support for users on older versions of Python,
-and these users should request for support from the relevant provider
-(eg: Linux distro community, cloud provider support channels, etc).
+Other operating systems and Python versions are not supported by pip's
+maintainers.
+
+Users who are on unsupported platforms should be aware that if they hit issues, they may have to resolve them for themselves. If they received pip from a source which provides support for their platform, they should request pip support from that source.
 
 [^python]: The `ensurepip` module was added to the Python standard library in Python 3.4.