Add a feature list to the README

README.md

@@ -2,11 +2,18 @@
 
 See https://git.caraus.tech/OSS/graphql.
 
+This is the core library that provides:
+
+- Parser for the query and schema languages, as well as a printer for the query
+  language (minimizer and pretty-printer).
+- Data structures to define a type system.
+- Executor (queries, mutations and subscriptions are supported).
+- Validation.
+
+## Documentation
+
 Report issues on the
 [bug tracker](https://git.caraus.tech/OSS/graphql/issues).
 
 API documentation is available through
 [Hackage](https://hackage.haskell.org/package/graphql).
-
-Further documentation will be made available in the
-[Wiki](https://git.caraus.tech/OSS/graphql/wiki).