Added release process notes/checklist/explanation

docs/release-process.md

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+# How to release
+
+When enough changes have accumulated, it is time to release new version of Catch. This document describes the proces in doing so, that no steps are forgotten. Note that all referenced scripts can be found in the `scripts/` directory.
+
+
+## Approval testing
+
+Catch's releases are primarily validated against output from previous release, stored in `projects/SelfTest/Baselines`. To validate current sources, build the SelfTest binary and pass it to the `approvalTests.py` script: `approvalTests.py <path/to/SelfTest>`.
+
+There should be no differences, as Approval tests should be updated when changes to Catch are made, but if there are, then they need to be manually reviewed and either approved (using `approve.py`) or Catch requires other fixes.
+
+
+## Incrementing version number
+
+Catch uses a variant of [semantic versioning](http://semver.org/), with breaking API changes (and thus major version increments) being very rare. Thus, the release will usually increment the patch version, when it only contains couple of bugfixes, or minor version, when it contains new functionality, or larger changes in implementation of current functionality. 
+
+After deciding which part of version number should be incremented, you can use one of the `*Release.py` scripts to perform the required changes to Catch.
+
+
+## Generate updated single-include header
+
+After updating version number, regenerate single-include header using `generateSingleHeader.py`.
+
+
+## Release notes
+
+Once a release is ready, release notes need to be written. They should summarize changes done since last release. For rough idea of expected notes see previous releases. Once written, release notes should be placed in `docs/release-notes.md`.
+
+
+## Commit and push update to GitHub
+
+After version number is incremented, single-include header is regenerated and release notes are updated, changes should be commited and pushed to GitHub. 
+
+
+## Release on GitHub
+
+After pushing changes to GitHub, GitHub release *needs* to be created. Tag version and release title should be same as the new version, description should contain the release notes for the current release. Single header version of `catch.hpp` *needs* to be attached as a binary, as that is where the official download link links to. Preferably it should use linux line endings.
+
+
+## vcpkg update
+
+As a last step, optionally update Microsoft's package manager [vcpkg](https://github.com/Microsoft/vcpkg) with Catch's new version. `updateVcpkgPackage.py` can do a lot of neccessary work for you, but it assumes that you have your fork of vcpkg checked out in a directory next to the directory, where you have checked out Catch.
+
+It creates a branch and commits neccessary changes, that you then should review, synchronize and open a PR against.