docs: parser's automata visualization

docs/src/cli.md

@@ -27,3 +27,31 @@ Instead of calling CLI manually you can setup your project to call the Rustemo
 compiler from `build.rs` script. You can read more in the [configuration
 section](configuration.md).
 ```
+
+## Visualizing parser's automata
+
+Besides providing a detailed information about the grammar and conflicts `rcomp`
+can produce a diagram of the parser's handle finding automaton.
+
+This can be used to investigate conflicts visually for smaller grammars.
+
+E.g. for ambiguous grammar `calc.rustemo`:
+
+```
+{{#include ./images/calc.rustemo}}
+```
+
+a diagram can be produced with:
+
+```
+rcomp --dot calc.rustemo
+```
+
+and either transformed to an image with [GraphViz dot
+tool](https://graphviz.org/docs/layouts/dot/) or opened directly using dot
+viewers like, for example, [xdot](https://github.com/jrfonseca/xdot.py).
+
+Here is how the diagram for the above grammar looks like. States marked with red
+are states with conflicts.
+
+![](./images/calc.dot.png)

docs/src/images/calc.rustemo

@@ -0,0 +1,8 @@
+E: E '+' E
+ | E '-' E
+ | num;
+
+terminals
+Plus: '+';
+Minus: '-';
+num: /\d+/;