add foundry banner in lesson

Author: 7i7o

pages/lessons/projects/6.mdx

@@ -136,6 +136,8 @@ The main focus of Foundry is that you don't need to use Javascript at all if you
 don't want to.
 All the tools are CLI commands. For tests and scripts, you only need Solidity!
 
+![foundry-banner.png](/assets/lessons/6/foundry-banner.png)
+
 These instructions are for Linux and MacOS. If you use Windows, we **strongly**
 recommend using
 WSL (Windows Subsystem for Linux), or else you will need to build the tools from