first-cut Contributor guide

CONTRIBUTING.md

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+# Contributor Guide
+
+## Git
+
+We use the `dev` branch for development. All feature branches should be based
+off `dev`.
+
+The `master` branch corresponds to the latest release. We deploy to [Julia
+General Registry][jgr] and `git tag -a` off `master`.
+
+## Running the unit tests (aka Julia tests)
+
+```sh
+git clone git@github.com:plotly/Dash.jl.git
+cd Dash.jl
+julia
+```
+
+```jl
+julia> import Pkg
+julia> Pkg.activate(".")
+julia> Pkg.instantiate()
+julia> Pkg.update()
+julia> Pkg.test()
+```
+
+To run the unit tests for multiple versions of Julia, we recommend using [`juliaup`][juliaup].
+
+## Running the integration tests
+
+The integration tests make use of the [`dash.testing`][testing] module part of
+the Python version of dash.
+
+Instructions on how to install the required system dependencies can be found
+in the [dash Contributor Guide][dash-cg].
+
+Then,
+
+```sh
+cd Dash.jl
+git clone --depth 1 https://github.com/plotly/dash.git -b dev dash-main
+python3 -m venv venv
+pip install --upgrade pip wheel
+cd dash-main && pip install -e .[ci,dev,testing] && cd ..dash
+pytest --headless --nopercyfinalize --percy-assets=test/assets/ test/integration/
+```
+
+Alternatively, one can run the integration tests using the same Docker
+image as for our CircleCI test runs. See the [Docker image guide][docker-test]
+for the details.
+
+## Updating the resources
+
+See the [Generate Dash.jl artifacts][resources].
+
+## Updating the CircleCI Docker image
+
+See the [Docker image guide][docker-update].
+
+## Code Style
+
+- indent with 4 spaces (no tabs),
+- no whitespaces at EOLs,
+- add a single newline at EOFs.
+
+See the [`lint.yml` workflow][lint] for the details.
+
+## Making a release
+
+**Please follow the step in order!** Running `git tag -a` before
+`@JuliaRegistrator register` will lead to a failed release!
+
+In the following steps, note that _X.Y.Z_ refers to the new version we are
+releasing.
+
+### step 1
+
+Make sure the [Julia unit tests][jltest] and [CircleCI integration tests][circlecI] are
+passing.
+
+### step 2
+
+Make a PR with `master` as the _base_ branch and `dev` as _compare_ branch.
+
+For consistency, name the PR: "Release X.Y.Z"
+
+### step 3
+
+Bump the `version` field in the `Project.toml` (following [semver][semver]) and then
+
+```sh
+git commit -m "X.Y.Z"
+```
+
+**N.B.** use `X.Y.Z` not `vX.Y.Z` in the commit message, the leading `v` is
+reserved for git tags.
+
+### step 4
+
+Wait for approval and then merge the PR onto `master`.
+
+### step 5
+
+Navigate on GitHub to the merge commit from the `master` branch e.g.
+
+<https://github.com/plotly/Dash.jl/commit/5ec76d9d3360f370097937efd06e5de5a6025888>
+
+and then add the following comment:
+
+```sh
+@JuliaRegistrator register branch=master
+```
+
+which tells the [Julia Registrator][registrator] to create a PR to the [General Registry][jgr] e.g.
+
+<https://github.com/JuliaRegistries/General/pull/77586>
+
+### step 6
+
+Wait for the Julia Registry PR to be merged.
+
+If things go well, this should be automatic!
+
+### step 7
+
+Off `master`, create and push a new git tag with:
+
+```sh
+git checkout master
+git tag -a vX.Y.Z   # N.B. leading `v`
+git push --tags
+```
+
+### step 8
+
+Go the [release page][releases] and create a new release,
+name it "Version X.Y.Z" for consistency and fill out sections:
+
+- _What's Changed_, which should include items for all the PRs merged since the last release
+- _New Contributor_, which should include mention of all the first-time contributors
+
+finally, place a [GitHub compare link][compare] between the last release and X.Y.Z e.g.
+
+<https://github.com/plotly/Dash.jl/compare/v1.1.2...v1.2.0>
+
+### step 9
+
+you are done :tada:
+
+[jgr]: https://github.com/JuliaRegistries/General
+[juliaup]: https://github.com/JuliaLang/juliaup
+[testing]: https://dash.plotly.com/testing#end-to-end-tests
+[dash-cg]: https://github.com/plotly/dash/blob/dev/CONTRIBUTING.md#tests
+[resources]: ./gen_resources/README.md
+[docker-test]: ./build/README.md#local-usage
+[docker-update]: ./build/README.md#how-to-update-the-docker-image
+[lint]: ./.github/workflows/lint.yml
+[jltest]: https://github.com/plotly/Dash.jl/actions/workflows/jl_test.yml?query=branch%3Adev
+[circlecI]: https://app.circleci.com/pipelines/github/plotly/Dash.jl?branch=dev
+[semver]: https://pkgdocs.julialang.org/v1/toml-files/#The-version-field
+[registrator]: https://github.com/JuliaRegistries/Registrator.jl
+[releases]: https://github.com/plotly/Dash.jl/releases
+[compare]: https://github.com/plotly/Dash.jl/compare/