Automated versioning using ChangeSets (#442)

* feat: install changesets

* chore: yarn changeset init

* chore: add l2geth to the workspace so it can be seen by changeset

* ci: add changeset release PR github action

https://github.com/changesets/action

* chore: set l2geth version to 0.2.0

.changeset/README.md

+# Changesets
+
+Hello and welcome! This folder has been automatically generated by `@changesets/cli`, a build tool that works
+with multi-package repos, or single-package repos to help you version and publish your code. You can
+find the full documentation for it [in our repository](https://github.com/changesets/changesets)
+
+We have a quick list of common questions to get you started engaging with this project in
+[our documentation](https://github.com/changesets/changesets/blob/main/docs/common-questions.md)

.changeset/config.json

+{
+  "$schema": "https://unpkg.com/@changesets/config@1.6.0/schema.json",
+  "changelog": "@changesets/cli/changelog",
+  "commit": false,
+  "linked": [],
+  "access": "public",
+  "baseBranch": "master",
+  "updateInternalDependencies": "patch",
+  "ignore": []
+}

.github/workflows/release.yml

+name: Release
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  release:
+    name: Release
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repo
+        uses: actions/checkout@master
+        with:
+          # This makes Actions fetch all Git history so that Changesets can generate changelogs with the correct commits
+          fetch-depth: 0
+
+      - name: Setup Node.js 12.x
+        uses: actions/setup-node@master
+        with:
+          node-version: 12.x
+
+      - name: Install Dependencies
+        run: yarn
+
+      - name: Create Release Pull Request
+        uses: changesets/action@master
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

l2geth/package.json

+{
+  "name": "@eth-optimism/l2geth",
+  "version": "0.2.0"
+}

package.json

@@ -4,6 +4,7 @@
   "license": "MIT",
   "workspaces": [
     "packages/*",
+    "l2geth",
     "integration-tests"
   ],
   "private": true,
@@ -18,5 +19,8 @@
     "lint": "yarn lerna run lint",
     "lint:ci": "yarn lerna run lint  --parallel --since origin/master",
     "lint:fix": "yarn lerna run lint:fix"
+  },
+  "dependencies": {
+    "@changesets/cli": "^2.16.0"
   }
 }