Add change 23 instructions

how_to/Change_23.md

@@ -0,0 +1,22 @@
+- tag: Resolve name to oid in argparse
+
+It's nice that we can create tags, but now let's actually make them usable from
+the CLI.
+
+In *base.py*, we'll create `get_oid` to resolve a "name" to an OID. A name can
+either be a ref (in which case `get_oid` will return the OID that the ref points
+to) or an OID (in which case `get_oid` will just return that same OID).
+
+Next, we'll modify the argument parser in *cli.py* to call `get_oid` on all
+arguments which are expected to be an OID. This way we can pass a ref there
+instead of an OID.
+
+At this point we can do something like:
+```
+$ ugit tag mytag d8d43b0e3a21df0c845e185d08be8e4028787069
+$ ugit log refs/tags/mytag
+# Will print log of commits starting at d8d43b0e...
+$ ugit checkout refs/tags/mytag
+# Will checkout commit d8d43b0e...
+etc...
+```