Added usage info to README

README.md

@@ -1,3 +1,16 @@
 # Project Euler solutions 
 Solutions to [Project Euler](https://projecteuler.net/) in various languages (mostly python).
 
+## Usage
+Compile with make
+```console
+$ make 
+```
+Solve all solved problems with
+```console
+$ ./main.py
+```
+or 
+```console
+$ python3 main.py
+```