Add CompUnit::Repository::Unknown

Part of #4591

Author: coke

doc/Type/CompUnit/Repository/Unknown.rakudoc

@@ -0,0 +1,37 @@
+=begin pod :kind("Type") :subkind("class") :category("domain-specific")
+
+=TITLE class CompUnit::Repository::Unknown
+
+=SUBTITLE CompUnit::Repository::Unknown
+
+=for code :preamble<role CompUnit::Repository {};>
+class CompUnit::Repository::FileSystem
+    does CompUnit::Repository
+    { }
+
+A L<C<CompUnit::Repository>|/type/CompUnit::Repository> placeholder that is used
+when the type of the Repository is unknown.
+in development situations. This is what is used by C<-I .> / C<-I lib> (which are
+actually C<-I file#.> and C<-I file#lib>) or C<use lib "."> / C<use lib "lib">.
+Unlike L<C<CompUnit::Repository::Installation>|/type/CompUnit::Repository::Installation>, this represents a single distribution.
+
+=head1 Methods
+
+=head2 method need
+
+=for code :method :preamble<method !precomp-stores() {...};>
+method need(
+    CompUnit::DependencySpecification $spec,
+    CompUnit::PrecompilationRepository $precomp?,
+    CompUnit::PrecompilationStore :@precomp-stores
+    --> CompUnit:D)
+
+This class passes any requests up the repository chain, and does not resolve them itself.
+
+=head2 method loaded
+
+    method loaded(--> Iterable:D)
+
+Always returns an empty L<C<Iterable>|/type/Iterable>.
+
+=end pod