aggiunta documentazione e programmi di esempio

doc/hello-world.txt

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+On the Elea 9003, we would program this in 27 characters (two instructions and one constant string); the rest of the memory would be empty.
+ 
+11 0017 # ø         Prints the memory contents from address 17 for length 11
+0X XXXX # 0          Stops the program                    
+HELLO WORLD     The constant at address 17
+ 
+And how to execute this program? Since it is short, we’ll type it directly in memory at address 1, so we type on the console keyboard:
+ 
+27 0001 # %
+
+Then we type the 27 characters on the console typewriter. Finally we branch to position 8, the address of the rightmost character of the first instruction, entering the following instruction from the console:
+ 
+)# 0008 # O
+ 
+This caused the program to be executed