Added K3s to the registry section of navbar
*** xref:installation/registry/github.adoc[Github Packages]
*** xref:installation/registry/gcr.adoc[Gcr.io]
*** xref:installation/registry/icr.adoc[IBM Container Registry]
+*** xref:installation/registry/k3s.adoc[K3s]
** xref:installation/scheduling.adoc[Pod scheduling]
* xref:running/running.adoc[Running]
** xref:running/dev-mode.adoc[Dev Mode]
