Add RunContext & VirtualMachine structres to Write your own VM se…

…ction (#12)

* Add RunContext

* Add VM structure

README.md

@@ -342,6 +342,37 @@ func (m *MemorySegmentManager) LoadData(ptr Relocatable, data *[]MaybeRelocatabl
 }
 ```
 
+### RunContext
+
+The RunContext keeps track of the vm's registers. Cairo VM only has 3 registers:
+
+- The program counter `Pc`, which points to the next instruction to be executed.
+- The allocation pointer `Ap`, pointing to the next unused memory cell.
+- The frame pointer `Fp`, pointing to the base of the current stack frame. When a new function is called, `Fp` is set to the current `Ap` value. When the function returns, `Fp` goes back to its previous value.
+
+We can represent it like this:
+
+```go
+type RunContext struct {
+	Pc memory.Relocatable
+	Ap memory.Relocatable
+	Fp memory.Relocatable
+}
+```
+
+### VirtualMachine
+With all of these types and structures defined, we can build our VM:
+
+```go
+type VirtualMachine struct {
+	runContext  RunContext
+	currentStep uint
+	segments    memory.MemorySegmentManager
+}
+```
+
+To begin coding the basic execution functionality of our VM, we only need these basic fields, we will be adding more fields as we dive deeper into this guide.
+
 ### Builtins
 
 TODO