build: add make convenience wrapper for guix scripts

contrib/guix/guix-codesign

@@ -35,8 +35,22 @@ EOF
 }
 
 if [ -z "$GUIX_SIGS_REPO" ]; then
-    cmd_usage
-    exit 1
+    echo "[HINT] Fork and clone the feather-sigs repo:"
+    echo "https://github.com/feather-wallet/feather-sigs"
+    echo ""
+
+    printf "Enter path to 'feather-sigs' repo: "
+    read -r GUIX_SIGS_REPO
+
+    if [ ! -d "${GUIX_SIGS_REPO}" ]; then
+        echo "Directory does not exist"
+        exit 1
+    fi
+
+    echo ""
+    echo "Next time, invoke this command as:"
+    echo "env GUIX_SIGS_REPO=${GUIX_SIGS_REPO} make codesign"
+    echo ""
 fi
 
 ################
@@ -73,7 +87,7 @@ fi
 
 if ! git -C "$GUIX_SIGS_REPO" diff-index --quiet HEAD -- && [ -z "$FORCE_DIRTY_WORKTREE" ]; then
     cat << EOF
-ERR: The DETACHED CODESIGNATURE git worktree is dirty, which may lead to broken builds.
+ERR: The FEATHER SIGS git worktree is dirty, which may lead to broken builds.
 
      Aborting...