Document release process (#5)

Since we've made the first proper release, let's document the process
so that it goes quicker next time.

Author: ilammy

RELEASING.md

@@ -0,0 +1,76 @@
+How to update to newer OpenSSL version, build, and publish a release.
+
+1. **Clone this repository.**
+
+   ```shell
+   git clone https://github.com/cossacklabs/openssl-apple
+   ```
+
+   Make sure you're on the `cossacklabs` branch.
+
+2. **Update OpenSSL version.**
+
+   The version number is in the [`Makefile`](Makefile).
+
+   Also update tarball checksums in [`build-libssl.sh`](build-libssl.sh).
+
+3. **Update platform configuration.**
+
+   Things like minimum OS SDK versions, architectures, etc.
+   You can find all this in the [`Makefile`](Makefile).
+
+4. **Build OpenSSL.**
+
+   ```shell
+   make
+   ```
+
+   This can take a while.
+   Not only it builds the library, this also packages it,
+   and updates the project specs.
+
+5. **Commit, tag, push the release.**
+
+   ```shell
+   git add carthage
+   git commit -S -e -m "OpenSSL 1.1.1g"
+   git tag -s -e -m "OpenSSL 1.1.1g" v1.1.107
+   git push origin cossacklabs # Push the branch
+   git push origin v1.1.107    # Push the tag
+   ```
+
+   Make will remind you how to do this.
+   (Use the correct versions there.)
+   Take care to make signed commits and tags, this is important for vanity.
+
+   Congratulations!
+   You have just published a broken Carthage package.
+
+6. **Publish GitHub release with binary framework files.**
+
+   Go to GitHub release page for the tag:
+
+   https://github.com/cossacklabs/openssl-apple/releases/tag/v1.1.107
+
+   press **Edit tag** and upload `*.zip` packages from `output` directory.
+
+   Also, describe the release, press the **Publish release** when done.
+
+   Congratulations!
+   You should have fixed the Carthage package with this.
+
+7. **Publish podspec.**
+
+   ```shell
+   pod trunk push cocoapods/CLOpenSSL.podspec
+   ```
+
+   This lints the podspec before publishing it.
+   If it does not lint then curse at CocoaPods and scrub the release.
+
+   Congratulations!
+   You have published a CocoaPods package.
+
+Actually, you have published all of the OpenSSL.
+Now is the time to go check if it *actually* works.
+You can use [Themis](https://github.com/cossacklabs/themis) for that.