📝 Populate readme

README.md

@@ -1,2 +1,63 @@
-# d3b-release-maker
-Tool to generate GitHub-based software releases
+# D3b Release Maker
+
+Tool to automate GitHub-based software releases for projects with the following
+characteristics:
+
+- Feature branching with merge-commits into master
+- Gitmoji-style PR messages
+- Semantic versioning tags for releases (<https://semver.org>)
+
+## Part 1: CLI that generates release notes and creates a PR on GitHub for review
+
+Install with pip:
+`pip install git+https://github.com/d3b-center/d3b-release-maker.git`
+
+Create a temporary auth token on GitHub and add it to your environment as
+`GH_TOKEN`.
+
+Then run: `release --help`
+
+## Part 2: GitHub Action that automates tagging releases and asset uploading
+
+Copy `.github/workflows/gh_releases.yml` into the same location in your
+repository. (Read more about GitHub Actions at <https://help.github.com/en/actions>)
+
+If you want to attach binary assets to your GitHub releases, add a
+`.github/prepare_assets.sh` script that generates your assets and
+then creates `.github/release_assets.txt` containing a list of the files you
+want to upload, one per line, in the order that you want them to appear.
+
+## What the parts do
+
+### What the CLI does
+
+When you run the `release build` command:
+
+1. The CLI looks at the most recent git tag that looks like a Semantic Version.
+2. Then it looks for all PRs that were merged into master after that tag which
+   do not themselves look like a release merge.
+3. Emojis at the start of the PR titles are grouped and counted according to
+   the gitmoji emoji guide (<https://gitmoji.carloscuesta.me>).
+4. Markdown is generated with links to PRs, merge commits, and committers and is
+   shown to the user.
+5. The user is prompted to provide a type of version update (major, minor,
+   patch) based on the shown list of changes, and a new version number is
+   generated.
+6. A fresh copy of your repository is cloned to a temporary location.
+7. The new changes list is added to the CHANGELOG.md file (one is created if
+   one doesn't already exist).
+8. An optional user-provided script is then run if you need to e.g. add the new
+   version number to files in your repository.
+9. All newly modified files are commited with a special release commit and
+   pushed to a special release branch, and a Pull Request into master is opened
+   on GitHub for review.
+
+### What the GitHub Action does
+
+When a special release branch is merged into master:
+
+1. Your repository is tagged with the new semantic version, and a GitHub
+   release is created with the contents of the just-merged Pull Request body.
+2. If a `.github/prepare_assets.sh` script exists, it is run.
+3. If a `.github/release_assets.txt` file exists, any files listed in it are
+   then uploaded to the GitHub release.