docs: mirror epidatr development doc

Author: dshemetov

DEVELOPMENT.md

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+## Setting up the development environment
+
+```r
+install.packages(c('devtools', 'pkgdown', 'styler', 'lintr')) # install dev dependencies
+devtools::install_deps(dependencies = TRUE) # install package dependencies
+devtools::document() # generate package meta data and man files
+devtools::build() # build package
+```
+
+## Validating the package
+
+```r
+styler::style_pkg() # format code
+lintr::lint_package() # lint code
+
+devtools::test() # test package
+devtools::check() # check package for errors
+```
+
+## Developing the documentation site
+
+The [documentation site](https://cmu-delphi.github.io/epidatr/) is built off of the `main` branch. The `dev` version of the site is available at https://cmu-delphi.github.io/epidatr/dev.
+
+The documentation site can be previewed locally by running in R
+
+```r
+pkgdown::build_site(preview=TRUE)
+```
+
+The `main` version is available at `file:///<local path>/epidatr/docs/index.html` and `dev` at `file:///<local path>/epidatr/docs/dev/index.html`.
+
+You can also build the docs manually and launch the site with python. From the terminal, this looks like
+```bash
+R -e 'devtools::document()'
+python -m http.server -d docs
+```
+
+For `pkgdown` to correctly generate both public (`main`) and `dev` documentation sites, the package version in `DESCRIPTION` on `dev` must have four components, and be of the format `x.x.x.9000`. The package version on `main` must be in the format `x.x.x`.
+
+The documentation website is updated on push or pull request to the `main` and `dev` branches.
+
+## Release process
+
+### Manual
+
+TBD
+
+### Automated (currently unavailable)
+
+The release consists of multiple steps which can be all done via the GitHub website:
+
+1. Go to [create_release GitHub Action](https://github.com/cmu-delphi/epidatr/actions/workflows/create_release.yml) and click the `Run workflow` button. Enter the next version number or one of the magic keywords (patch, minor, major) and hit the green `Run workflow` button.
+2. The action will prepare a new release and will end up with a new [Pull Request](https://github.com/cmu-delphi/epidatr/pulls)
+3. Let the code owner review the PR and its changes and let the CI check whether everything builds successfully
+4. Once approved and merged, another GitHub action job starts which automatically will
+   1. create a git tag
+   2. create another [Pull Request](https://github.com/cmu-delphi/epidatr/pulls) to merge the changes back to the `dev` branch
+   3. create a [GitHub release](https://github.com/cmu-delphi/epidatr/releases) with automatically derived release notes
+5. Release to CRAN