Add CHANGELOG file

This should be used to fill in entries for new release, hopefully
done as they are added. Since this is the first one, it details
changes in 2.2 from 2.1.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

CHANGELOG

@@ -0,0 +1,30 @@
+liburing-2.2 release
+
+- Support non-libc builds.
+- Optimized syscall handling for x86-64/x86/aarch64.
+- IOPOLL fixes.
+- Enable non-lib function calls for fast path functions.
+- Add support for multishot accept.
+- io_uring_register_files() will set RLIMIT_NOFILE if necessary.
+- Add support for registered ring fds, io_uring_register_ring_fd(),
+  reducingthe overhead of an io_uring_enter() system call.
+- Add support for the message ring opcode.
+- Add support for newer request cancelation features.
+- Add support for IORING_SETUP_COOP_TASKRUN, which can help reduce the
+  overhead of io_uring in general. Most applications should set this flag,
+  see the io_uring_enter.3 man page for details.
+- Add support for registering a sparse buffer and file set.
+- Add support for a new buffer provide scheme, see
+  io_uring_register_buf_ring.3 for details.
+- Add io_uring_submit_and_wait_timeout() for submitting IO and waiting
+  for completions with a timeout.
+- Add io_uring_prep_{read,write}v2 prep helpers.
+- Add io_uring_prep_close_direct() helper.
+- Add support for SQE128 and CQE32, which are doubly sized SQE and CQE
+  rings. This is needed for some cases of the new IORING_OP_URING_CMD,
+  notably for NVMe passthrough.
+- ~5000 lines of man page additions, including adding 87 new man pages.
+- Synced with the 5.19 kernel release, supporting all the features of
+  5.19 and earlier.
+- 23 new regression test cases, and ~6000 lines of new tests in general.
+- General optimizations and fixes.