add some comments

src/extract.zig

@@ -2,24 +2,37 @@ const std = @import("std");
 const builtin = @import("builtin");
 const tools = @import("tools.zig");
 
+const xz = std.compress.xz;
+const tar = std.tar;
+
+/// extract tar.xz to dir
 pub fn extract_tarxz_to_dir(allocator: std.mem.Allocator, out_dir: std.fs.Dir, file: std.fs.File) !void {
     var buffered_reader = std.io.bufferedReader(file.reader());
-    var decompressed = try std.compress.xz.decompress(allocator, buffered_reader.reader());
+
+    var decompressed = try xz.decompress(allocator, buffered_reader.reader());
     defer decompressed.deinit();
-    try std.tar.pipeToFileSystem(out_dir, decompressed.reader(), .{ .mode_mode = .executable_bit_only, .strip_components = 1 });
+
+    try tar.pipeToFileSystem(
+        out_dir,
+        decompressed.reader(),
+        .{ .mode_mode = .executable_bit_only, .strip_components = 1 },
+    );
 }
 
+/// extract zip to directory
 pub fn extract_zip_dir(out_dir: std.fs.Dir, file: std.fs.File) !void {
     var arena = std.heap.ArenaAllocator.init(tools.get_allocator());
     defer arena.deinit();
 
     const allocator = arena.allocator();
+    // for decompressing zig, we need to make a temp directory
     const tmp_path = try tools.get_zvm_path_segment(allocator, "tmpdir");
     defer std.fs.deleteDirAbsolute(tmp_path) catch unreachable;
 
     try std.fs.makeDirAbsolute(tmp_path);
     var tmp_dir = try std.fs.openDirAbsolute(tmp_path, .{ .iterate = true });
 
+    // extract zig
     try std.zip.extract(tmp_dir, file.seekableStream(), .{});
 
     var iterate = tmp_dir.iterate();