add tahoe-great-black-swamp and tahoe-chk dependencies

These give us the network protocol for downloading, the framing protocol for
decoding, and the cryptographic protocol for decrypting

flake.nix

@@ -30,7 +30,12 @@
       };
     in {
       checks = hslib.checks {};
-      devShells = hslib.devShells {};
+      devShells = hslib.devShells {
+        extraBuildInputs = pkgs:
+          with pkgs; [
+            zlib
+          ];
+      };
       packages = hslib.packages {};
       apps.hlint = hslib.apps.hlint {};
 

gbs-downloader.cabal

@@ -74,7 +74,10 @@ library
   -- other-extensions:
 
   -- Other library packages from which modules are imported.
-  build-depends:    base ^>=4.14.3.0
+  build-depends:
+    , base                     ^>=4.14.3.0
+    , tahoe-chk
+    , tahoe-great-black-swamp
 
   -- Directories containing source files.
   hs-source-dirs:   src