[whitespace] README: more details on continuous integration.

README.md

@@ -1,9 +1,19 @@
-### Testing
+### Continuous Integration
 
 | Drone | Travis | Cirrus |
 | -------- | ------ | ------- |
 | [![Build Status](https://cloud.drone.io/api/badges/concurrencykit/ck/status.svg)](https://cloud.drone.io/concurrencykit/ck) | [![Build Status](https://travis-ci.org/concurrencykit/ck.svg)](https://travis-ci.org/concurrencykit/ck) | [![Build Status](https://api.cirrus-ci.com/github/concurrencykit/ck.svg?branch=master)](https://cirrus-ci.com/github/concurrencykit/ck) |
 
+Compilers tested in the past include gcc, clang, cygwin, icc, mingw32, mingw64 and suncc across all supported architectures. All new architectures are required to pass the integration test and under-go extensive code review.
+
+Continuous integration is currently enabled for the following targets:
+ * `darwin/clang/x86-64`
+ * `freebsd/clang/x86-64`
+ * `linux/gcc/arm64`
+ * `linux/gcc/x86-64`
+ * `linux/clang/x86-64`
+ * `linux/clang/ppc64le`
+
 ### Build
 
 * Step 1.