repo: add swift-docc to the manifest

Author: hjyamauchi

default.xml

@@ -19,6 +19,7 @@
   <project remote="github" name="apple/swift-corelibs-foundation" path="swift-corelibs-foundation" />
   <project remote="github" name="apple/swift-corelibs-xctest" path="swift-corelibs-xctest" />
   <project remote="github" name="apple/swift-crypto" path="swift-crypto" revision="refs/tags/2.5.0" />
+  <project remote="github" name="apple/swift-docc" path="swift-docc" />
   <project remote="github" name="apple/swift-docc-plugin" path="swift-docc-plugin" revision="refs/tags/1.0.0" />
   <project remote="github" name="apple/swift-docc-symbolkit" path="swift-docc-symbolkit" />
   <project remote="github" name="apple/swift-driver" path="swift-driver" />