Update readme with build instructions

README.md

@@ -1 +1,14 @@
 Made for my studies on low-level programming
+
+---
+
+Clone and cd:
+`git clone https://github.com/synt-xerror/assembly-calculator`
+`cd assembly-calculator`
+
+Assemble using `nasm` and link using `ld`:
+`nasm -f elf64 calculator.s -o calculator.o`
+`ld calculator.o -o calculator`
+
+Run:
+`./calculator`