Add a root documentation node

docs/Documentation.md

@@ -0,0 +1,5 @@
+# Documentation
+
+Browse the documentation tree by clicking on the links on the left.  Please
+write to us at [streamly@composewell.com](mailto:streamly@composewell.com) if
+you see something incorrect.

docs/streamly-docs.cabal

@@ -16,6 +16,7 @@ build-type:         Simple
 -------------------------------------------------------------------------------
 
 extra-doc-files:
+  *.md
   User/*.md
   User/Tutorials/*.md
   User/Tutorials/*.link

streamly.cabal

@@ -143,6 +143,7 @@ extra-doc-files:
     CHANGELOG.md
     README.md
     benchmark/README.md
+    docs/*.md
     docs/Developer/Benchmarks.md
     docs/Developer/*.png
     docs/Developer/*.md