Begin to explain mutation operators

README.md

@@ -5,7 +5,7 @@ mutant
 [![Dependency Status](https://gemnasium.com/mbj/mutant.png)](https://gemnasium.com/mbj/mutant)
 [![Code Climate](https://codeclimate.com/github/mbj/mutant.png)](https://codeclimate.com/github/mbj/mutant)
 
-Mutant is a mutation testing tool for ruby. It aims to be better than existing mutation testers.
+Mutant is a mutation testing tool for ruby.
 
 The idea is that if code can be changed and your tests do not notice, either that code isn't being covered
 or it does not have a speced side effect.
@@ -50,6 +50,32 @@ The 0.2 series is stable but has outdated dependencies. The 0.3 series is in bet
 gem install mutant --pre
 ```
 
+Mutations
+---------
+
+Mutant supports a very wide range of mutation operators. Listing them all detailed would blow this document up.
+
+It is planned to parse a list of mutation operators from the source. In the meanwhile pls refer to the
+[code](https://github.com/mbj/mutant/tree/master/lib/mutant/mutator/node) each subclass of `Mutant::Mutator::Node` 
+emits around 3-6 mutations.
+
+Currently mutant explicitly covers the majority of rubies complex nodes that often occur in method bodies.
+
+A some stats from the [axiom](https://github.com/dkubb/axiom) library:
+
+```
+Subjects:  417       # Amount of subjects being mutated (currently only methods)
+Mutations: 5442      # Amount of mutations mutant generated (~13 mutations per method)
+Kills:     5385      # Amount of successfully killed mutations
+Runtime:   1898.11s  # Total runtime
+Killtime:  1884.17s  # Time spend killing mutations
+Overhead:  0.73%
+Coverage:  98.95%    # Coverage score
+Alive:     57        # Amount of alive mutations.
+```
+
+Nodes still missing a dedicated mutator are handled via the [Generic](https://github.com/mbj/mutant/blob/master/lib/mutant/mutator/node/generic.rb) mutator.
+
 Examples
 --------