Add change 28 to instructions

how_to/Change_28.md

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+- k: Render graph
+
+`k` is supposed to be a visualization tool, but so far we've just printed a
+bunch of OIDs... Now comes the visualization part!
+
+There's a convenient file format called "dot" that can describe a graph. This is
+a textual format. We'll generate a graph of all commits and refs in dot format
+and then visualize it using the "dot" utility that comes with Graphviz.
+
+(If you're unfamiliar with dot or Graphviz please look it up online.)
+
+The graph will contain a node for each commit, that points to the parent commit.
+The graph will also contain a node for each ref, which points to the relevant
+commit.
+
+At this point, `ugit k` is fully functional and I encourage you to play with it.
+Create a crazy branching history and a bunch of tags and see for yourself that
+`ugit k` can draw all that visually.