Add a section about publishing

doc/how-to-source-packages.rst

@@ -293,6 +293,13 @@ picked up from the source code repository instead of from Hackage.
          location: https://github.com/haskell/vector.git
          subdir:   vector
 
+*Source code* as a package publisher
+------------------------------------
+
+If you are publishing a package to Hackage, you'll first need to create a
+``.tar.gz`` archive of your package's source code. This is done with the ``cabal
+sdist`` command that names archives after package name and version.
+
 .. _pkg-consumers:
 
 .. [#] Also known as a version control system (VCS) repository.