Add build instructions

README.md

@@ -1,3 +1,19 @@
 # Biome box
 
 Experimental project for map creation with biomes.
+
+# Build
+
+You need `make` and `SDL1` to build this project.
+
+Example on Ubuntu :
+```sh
+$ sudo apt install make g++ libsdl-dev
+$ make
+```
+
+To execute :
+```sh
+$ make exec
+```
+