Add table of contents to README

README.md

@@ -2,6 +2,25 @@
 
 # ![Build your own X](feynman.png)
 
+## Table of contents 
+
+- [3D Renderer](#build-your-own-3d-renderer)
+- [Blockchain / Cryptocurrency](#build-your-own-blockchain-cryptocurrency)
+- [Bot](#build-your-own-bot)
+- [Database](#build-your-own-database)
+- [Front-end Framework / Library](#build-your-own-front-end-framework-library)
+- [Docker](#build-your-own-docker)
+- [Game](#build-your-own-game)
+- [Git](#build-your-own-git)
+- [Neural Network](#build-your-own-neural-network)
+- [Network Stack](#build-your-own-network-stack)
+- [Operating System](#build-your-own-operating-system)
+- [Programming Language](#build-your-own-programming-language)
+- [Regex Engine](#build-your-own-regex-engine)
+- [Shell](#build-your-own-shell)
+- [Template Engine](#build-your-own-template-engine)
+- [Web Server](#build-your-own-web-server)
+
 #### Build your own `3D Renderer`
 
 * [**C++**: *Introduction to Ray Tracing: a Simple Method for Creating 3D Images*](https://www.scratchapixel.com/lessons/3d-basic-rendering/introduction-to-ray-tracing/how-does-it-work)