CI: build.sh: upd NIX_PATH doc

M  .travis.yml
M  build.sh

.travis.yml

@@ -31,7 +31,6 @@ env:
     ###
     #
     # - rev=nixos-unstable
-    # # NOTE: Switching into Nixpkgs revision
     # - NIX_PATH="nixpkgs=https://github.com/nixos/nixpkgs/archive/$rev.tar.gz"
     # NOTE: Project/binary name
     - name='hnix'

build.sh

@@ -21,6 +21,7 @@ GHCVERSION=${GHCVERSION:-'ghc8101'}
 #   ...
 #   }
 rev=${rev:-'nixpkgs-unstable'}
+# If NIX_PATH not imported - construct it from `rev`
 NIX_PATH=${NIX_PATH:-"nixpkgs=https://github.com/nixos/nixpkgs/archive/$rev.tar.gz"}
 export NIX_PATH
 name=${name:-'defaultProjectName'}