Handle submodule line

Fixes #60

src/delta.rs

@@ -114,13 +114,19 @@ where
                 handle_hunk_meta_line(&mut painter, &line, config)?;
                 continue;
             }
-        } else if source == Source::DiffUnified && line.starts_with("Only in ") {
+        } else if source == Source::DiffUnified && line.starts_with("Only in ")
+            || line.starts_with("Submodule ")
+        {
             // Additional FileMeta cases:
             //
             // 1. When comparing directories with diff -u, if filenames match between the
             //    directories, the files themselves will be compared. However, if an equivalent
             //    filename is not present, diff outputs a single line (Only in...) starting
             //    indicating that the file is present in only one of the directories.
+            //
+            // 2. Git diff emits lines describing submodule state such as "Submodule x/y/z contains
+            //    untracked content"
+
             state = State::FileMeta;
             painter.paint_buffered_lines();
             if config.opt.file_style != cli::SectionStyle::Plain {