Add documentation about unsupported firewall use cases. (#297)

ref https://veracode.atlassian.net/browse/SFP-165

Author: mhorner-vera

docs/package_firewall/about.md

@@ -53,6 +53,11 @@ registries:
 Phylum supports sending out notifications whenever a package fails analysis. To
 receive those notifications, you can [setup webhooks].
 
+### Currently Unsupported
+
+If you don't find what you're looking for here, please also see the
+[Currently Unsupported] page.
+
 ### Frequently Asked Questions
 
 See the [FAQ] for common questions about using the package firewall.
@@ -68,3 +73,4 @@ See the [FAQ] for common questions about using the package firewall.
 [PyPI]: ./pypi.md
 [RubyGems]: ./rubygems.md
 [FAQ]: ./faq.md
+[Currently Unsupported]: ./unsupported.md

docs/package_firewall/unsupported.md

@@ -0,0 +1,12 @@
+# Currently Unsupported
+
+## Artifact Repositories
+
+### Azure Artifacts
+
+Azure Artifacts provides support for storing packages from registries with its
+"upstream sources" feature. You can provide a custom registry URL, but there is
+no support for credentials, which is required for Phylum Package Firewalls.
+
+They also only support custom registries for NPM, which limits its potential
+usefulness.

site/sidebars.js

@@ -138,6 +138,7 @@ const sidebars = {
         'package_firewall/rubygems',
         'package_firewall/api',
         'package_firewall/faq',
+        'package_firewall/unsupported',
       ],
     },
     {