Add a RELEASES.md file to track release notes (#1011)

This is intended to be a form of release notes for wasmtime where we can
keep track of what's changed over time in a more dense way than `git
log` that should be interesting for most users.

RELEASES.md

@@ -0,0 +1,50 @@
+# Wasmtime Releases
+
+--------------------------------------------------------------------------------
+
+## 0.12.0
+
+Released 2020-02-26.
+
+### Added
+
+* Support for the [WebAssembly text annotations proposal][annotations-proposal]
+  has been added.
+  [#998](https://github.com/bytecodealliance/wasmtime/pull/998)
+
+* An initial C API for instantiating WASI modules has been added.
+  [#977](https://github.com/bytecodealliance/wasmtime/pull/977)
+
+* A new suite of `Func::getN` functions have been added to the `wasmtime` API to
+  call statically-known function signatures in a highly optimized fashion.
+  [#955](https://github.com/bytecodealliance/wasmtime/pull/955)
+
+* Initial support for profiling JIT code through perf jitdump has been added.
+  [#360](https://github.com/bytecodealliance/wasmtime/pull/360)
+
+* More CLI flags corresponding to proposed WebAssembly features have been added.
+  [#917](https://github.com/bytecodealliance/wasmtime/pull/917)
+
+[annotations-proposal]: https://github.com/webassembly/annotations
+
+### Changed
+
+* The `wasmtime` CLI as well as embedding API will optimize WebAssembly code by
+  default now.
+  [#973](https://github.com/bytecodealliance/wasmtime/pull/973)
+  [#988](https://github.com/bytecodealliance/wasmtime/pull/988)
+
+* The `verifier` pass in Cranelift is now no longer run by default when using
+  the embedding API.
+  [#882](https://github.com/bytecodealliance/wasmtime/pull/882)
+
+### Fixed
+
+* Code caching now accurately accounts for optimization levels, ensuring that if
+  you ask for optimized code you're not accidentally handed unoptimized code
+  from the cache.
+  [#974](https://github.com/bytecodealliance/wasmtime/pull/974)
+
+* Automated releases for tags should be up and running again, along with
+  automatic publication of the `wasmtime` Python package.
+  [#971](https://github.com/bytecodealliance/wasmtime/pull/971)