Add usage section to README

README.md

@@ -1,3 +1,30 @@
 # parzig
 
 A Parquet parser written in Zig using only the standard library.
+
+## Usage
+
+```zig
+const parzig = @import("parzig");
+
+var file = try parzig.parquet.File.read(allocator, &file_reader);
+defer file.deinit();
+
+var rg = file.rowGroup(0);
+
+// Static typing: specify type at compile time
+const values = try rg.readColumn(i64, 0);
+const nullable = try rg.readColumn(?i64, 1);
+
+// Dynamic typing: type determined at runtime
+const dynamic = try rg.readColumnDynamic(0);
+switch (dynamic) {
+    .int64 => |data| // ...
+    .byte_array => |data| // ...
+    // ...
+}
+
+// Nested types
+const list = try rg.readListColumn(i32, 0);
+const map = try rg.readMapColumn([]const u8, i64, 0, 1);
+```