Updated cabal file with instructions on split modules

md-to-html.cabal

@@ -53,7 +53,13 @@ extra-doc-files:    CHANGELOG.md
 common warnings
     ghc-options: -Wall
 
-executable md-to-html
+library
+   hs-source-dirs:   src
+   exposed-modules: MdToHTML
+   build-depends:    base ^>=4.19.1.0,
+                      HUnit
+
+executable md-to-html-runner
     -- Import common warning flags.
     import:           warnings
 
@@ -67,7 +73,9 @@ executable md-to-html
     -- other-extensions:
 
     -- Other library packages from which modules are imported.
-    build-depends:    base ^>=4.19.1.0
+    build-depends:    base ^>=4.19.1.0,
+                      md-to-html,
+                      HUnit
 
     -- Directories containing source files.
     hs-source-dirs:   app