chore: activate the release please bot and add release documentation (#55)

Author: capachino

.github/release-please.yml

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+handleGHRelease: true
+manifest: true

docs/releases.md

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+# Release Process
+
+This document outlines the release process for this project, which is automated using a combination of [Release Please](https://github.com/googleapis/release-please) and GitHub Actions.
+
+## Overview
+
+The release process is triggered by merging a "Release PR" to the `main` branch. This PR is automatically created and updated by the [Release Please bot](https://github.com/apps/release-please).
+
+## Release Please Workflow
+
+1.  **Conventional Commits:** This repository follows the [Conventional Commits](https://www.conventionalcommits.org/) specification. The commit messages are used by Release Please to determine the next version number and to generate a changelog.
+
+2.  **Release PR:** When new commits that should trigger a release (e.g., `feat:`, `fix:`) are pushed to the `main` branch, the Release Please bot will create or update a pull request. This "Release PR" includes:
+    *   A version bump in the `gemini-extension.json` and other relevant files.
+    *   An updated `CHANGELOG.md` with the latest changes.
+
+3.  **Triggering a Release:** To create a new release, a repository maintainer simply needs to merge the Release PR.
+    *   The [Release Please bot](https://github.com/apps/release-please) creates a new GitHub Release with the version number from the merged PR.
+    *   The changelog from the Release PR is used as the release notes.
+
+## GitHub Actions Workflow
+
+The `package-and-upload-assets.yml` workflow then packages the extension and uploads it as a release asset to the GitHub Release.