Add documentation to README

Author: kazk

README.md

@@ -1,3 +1,37 @@
 # Hspec Codewars
 
 Utility functions for testing on Codewars with Hspec.
+
+## Functions
+
+### Blacklisting
+
+```haskell
+solutionShouldHide :: Hidden -> Expectation
+
+-- solutionShouldHide $ FromModule "Prelude" "head"
+```
+Check that solution hides a module or a symbol from a module.
+
+```haskell
+solutionShouldHideAll :: [Hidden] -> Expectation
+
+-- solutionShouldHideAll [FromModule "Prelude" "head", Module "Data.Set"]
+```
+Check that solution hides all of given modules and symbols.
+
+### Approximate Equality
+
+```haskell
+shouldBeApprox :: (Fractional a, Ord a, Show a) => a -> a -> Expectation
+
+-- sqrt 2.0 `shouldBeApprox` (1.4142135 :: Double)
+```
+Predefined approximately equal expectation with error margin `1e-6`.
+
+```haskell
+shouldBeApproxPrec :: (Fractional a, Ord a, Show a) => a -> a -> a -> Expectation
+
+-- shouldBeApprox' = shouldBeApproxPrec 1e-9
+```
+Create approximately equal expectation with margin.