Added build instructions

README.md

@@ -1,3 +1,9 @@
 # Constrained Zig
 
 Check out the code [here](https://github.com/LukasPietzschmann/zigchr).
+
+## Build it
+1. You need to clone using the `--recursive` switch
+2. Just call `latexmk` on the `talk.tex` file
+
+If you don't want to build the slides yourself, you can also download them [here](https://raw.githubusercontent.com/LukasPietzschmann/zigtoberfest-talk/build/talk.pdf) or [here](https://github.com/LukasPietzschmann/zigtoberfest-talk/blob/build/talk.pdf).