Adds approximation example to README

README.md

@@ -63,6 +63,15 @@ describe(@"test name derived matching", ^{
 SpecEnd
 ```
 
+### Approximation support
+
+If for some reason you want to specify a tolerance for your test, you can use either named or unnamed matchers, where the `tolerance` parameter is a `CGFloat` in the interval `[0, 1]` and it represents the minimum ratio of unmatched points by the total number of points in your snapshot. In the example below, a tolerance of `0.01` means our `view` could be up to `1%` different from the reference image.
+
+``` Objective-C
+expect(view).to.haveValidSnapshotWithTolerance(0.01);
+expect(view).to.haveValidSnapshotNamedWithTolerance(@"unique snapshot name", 0.01);
+```
+
 ### Sane defaults
 
 `EXPMatchers+FBSnapshotTest` will automatically figure out the tests folder, and [add a reference image](https://github.com/dblock/ios-snapshot-test-case-expecta/blob/master/EXPMatchers%2BFBSnapshotTest.m#L84-L85) directory, if you'd like to override this, you should include a `beforeAll` block setting the `setGlobalReferenceImageDir` in each file containing tests.