Add RELEASE.md document

RELEASE.md

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+# Release
+
+This document is primarily targeted towards Deephaven CSV release managers.
+It is meant to contain the necessary instructions for executing a Deephaven CSV release.
+
+Please be sure to read and understand this document in full before proceeding with a release.
+If you have any questions or concerns about any of the commands, please reach out.
+
+## Jar artifacts
+
+The deephaven-csv release process consists of releasing two jars to [Maven Central](https://repo1.maven.org/maven2/io/deephaven/).
+
+* [io.deephaven:deephaven-csv](https://repo1.maven.org/maven2/io/deephaven/deephaven-csv/)
+* [io.deephaven:deephaven-csv-fast-double-parser](https://repo1.maven.org/maven2/io/deephaven/deephaven-csv-fast-double-parser/)
+
+## Release process
+
+The majority of the release procedure is executed by the [publish.yml workflow](./.github/workflows/publish.yml).
+It is kicked off by a push to a branch name that matches `release/v*`.
+Please familiarize yourself with the steps in that workflow.
+
+### 0. Poll Deephaven CSV team
+
+Ensure you are proceeding with a known release, and there aren't any blockers.
+
+### 1. Repository prerequisites
+
+These release notes assume that the Deephaven CSV repository `git@github.com:deephaven/deephaven-csv.git` is referenced as the remote named `upstream`.
+Please ensure your local repository is set up as such, or that you replace any commands with the appropriately named remote:
+
+```shell
+$ git remote get-url upstream
+git@github.com:deephaven/deephaven-csv.git
+```
+
+### 2. Create release branch and commit version bump
+
+Ensure you are up-to-date with `upstream/main`, or at the commit that you want to start a new release from.
+If you are unsure what commit to start from, please ask.
+Most of the time, the main branch will be referencing a `-SNAPSHOT` version, and we'll want to update this to a non-snapshot version.
+Please double-check you are on the version you expect to be releasing.
+The releases have so far proceeded with branches named `releave/vX.Y.Z`, where `X.Y.Z` is the version number (this isn't a technical requirement), please replace `X.Y.Z` with the appropriate version.
+
+```shell
+$ git fetch upstream
+$ git checkout upstream/main
+$ git checkout -b release/vX.Y.Z
+$ # edit gradle.properties, remove -SNAPSHOT
+$ git add gradle.properties
+$ git commit -m "Bump to version X.Y.Z"
+```
+
+### 3. Push to upstream
+
+Triple-check things look correct, the release is a "GO", and then start the release process by pushing the release branch to upstream:
+
+```shell
+$ git show release/vX.Y.Z
+$ git push -u upstream release/vX.Y.Z
+```
+
+### 4. Monitor release
+
+The release will proceed with [GitHub Actions](https://github.com/deephaven/deephaven-csv/actions/workflows/publish.yml).
+
+### 5. Maven Central jars
+
+The jars are put into a [Maven Central Repository Manager](https://s01.oss.sonatype.org) staging repository.
+You'll need your own username and password to sign in (to ensure auditability).
+
+If any late-breaking issues are found during the release process, but the Maven Central jars have not been released from staging, the release process can be re-done.
+Once the jars are officially released from the staging repository, they are released "forever".
+
+When ready, the staging repository will need to be "Closed" and then "Released".
+Once the staging repository has been "Released", there is no going back.
+
+The jars will be visible after release at [https://repo1.maven.org/maven2/io/deephaven/](https://repo1.maven.org/maven2/io/deephaven/).
+Sometimes it takes a little bit of time for the jars to appear.
+
+### 6. Tag upstream
+
+The `vX.Y.Z` tag is primarily meant for an immutable reference point in the future.
+It does not kick off any additional jobs.
+The release should only be tagged _after_ the Maven Central staging repository has been "Released".
+
+```shell
+$ git tag vX.Y.Z release/vX.Y.Z
+$ git show vX.Y.Z
+$ git push upstream vX.Y.Z
+```
+
+### 7. Prepare next development iteration
+
+The main branch is explicitly updated (instead of going through a squash and merge PR process):
+
+```shell
+$ git checkout main
+$ git merge --ff-only vX.Y.Z
+# edit gradle.properties, bump version, add -SNAPSHOT
+# Do a find and replace for old version, replace with new version (across READMEs)
+$ ...
+$ git add .
+$ git status -uno
+$ git commit -m "Version A.B.C-SNAPSHOT"
+$ git push -u upstream main
+```
+
+The release branch can be deleted locally and remotely.
+
+### 8. GitHub release
+
+Create a new [GitHub release](https://github.com/deephaven/deephaven-csv/releases/new) and use the `vX.Y.Z` tag as reference.
+
+The convention is to have the Release title of the form `vX.Y.Z` and to autogenerate the release notes in comparison to the previous release tag.
+
+Hit the GitHub "Publish release" button.