docs: add additional design systems (#4512)

Author: nmerget

docs/research-other-design-systems.md

@@ -46,6 +46,10 @@ We'd like to maintain a list of other design systems that might be interesting f
     - React
 - [GOV.UK Design System](https://design-system.service.gov.uk/)
 - [Paste](https://paste.twilio.design/)
+- [Swiss Post](https://github.com/swisspost/design-system):
+    - Web Components / StencilJS
+- [Solid Design](https://github.com/solid-design-system/solid):
+    - Web Components
 
 ## Design System "registries" / overviews