update readme with json example

README.md

@@ -26,6 +26,8 @@ Here's what works:
   dispatching on the HTTP path 
 - **[serve](examples/serve/serve.zig)**: the traditional static web
   server with optional dynamic request handling
+- **[hello_json](examples/hello_json/hello_json.zig)**: serves you json
+  dependent on HTTP path
 
 I'll continue wrapping more of facil.io's functionality and adding stuff to zap
 to a point where I can use it as the JSON REST API backend for my current
@@ -138,7 +140,6 @@ pub fn main() !void {
 
 ### [routes](examples/routes/routes.zig)
 
-
 ```zig
 const std = @import("std");
 const zap = @import("zap");
@@ -202,3 +203,78 @@ pub fn main() !void {
     });
 }
 ```
+
+### [hello_json](examples/hello_json/hello_json.zig)
+
+```zig 
+const std = @import("std");
+const zap = @import("zap");
+
+const User = struct {
+    first_name: ?[]const u8 = null,
+    last_name: ?[]const u8 = null,
+};
+
+fn on_request(r: zap.SimpleRequest) void {
+    if (!std.mem.eql(u8, r.method.?, "GET"))
+        return;
+
+    // /user/n
+    if (r.path) |the_path| {
+        if (the_path.len < 7 or !std.mem.startsWith(u8, the_path, "/user/"))
+            return;
+
+        const user_id: usize = @intCast(usize, the_path[6] - 0x30);
+        const user = users.get(user_id);
+
+        var json_to_send: []const u8 = undefined;
+        if (stringify(user, .{})) |json| {
+            json_to_send = json;
+        } else {
+            json_to_send = "null";
+        }
+        std.debug.print("<< json: {s}\n", .{json_to_send});
+        r.setContentType(.JSON);
+        _ = r.sendBody(json_to_send);
+    }
+}
+
+const UserMap = std.AutoHashMap(usize, User);
+
+var users: UserMap = undefined;
+fn setupUserData(a: std.mem.Allocator) !void {
+    users = UserMap.init(a);
+    try users.put(1, .{ .first_name = "renerocksai" });
+    try users.put(2, .{ .first_name = "Your", .last_name = "Mom" });
+}
+
+fn stringify(value: anytype, options: std.json.StringifyOptions) ?[]const u8 {
+    var buf: [100]u8 = undefined;
+    var fba = std.heap.FixedBufferAllocator.init(&buf);
+    var string = std.ArrayList(u8).init(fba.allocator());
+    if (std.json.stringify(value, options, string.writer())) {
+        return string.items;
+    } else |_| { // error
+        return null;
+    }
+}
+
+pub fn main() !void {
+    var a = std.heap.page_allocator;
+    try setupUserData(a);
+    var listener = zap.SimpleHttpListener.init(.{
+        .port = 3000,
+        .on_request = on_request,
+        .log = false,
+    });
+    try listener.listen();
+
+    std.debug.print("Listening on 0.0.0.0:3000\n", .{});
+
+    // start worker threads
+    zap.start(.{
+        .threads = 2,
+        .workers = 2,
+    });
+}
+```