Add change 02 instructions

how_to/Change_02.md

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+- cli: Add argument parser
+
+The real Git executable has multiple sub-commands, like 'git init', 'git commit',
+etc. Let's use Python's built-in argument parser argparse to implement sub-commands.
+
+You can see on the other side which changes were made. Now we can run 'ugit init'
+and see "Hello, World!" printed out.