chore: add prerelease script (#876)

* chore: add prerelease script

* Update prerelease.md

* Update prerelease.sh

* Update prerelease.sh

* chore: address review

* update instruction

* alias 'run version' to make it clear we're running docs version

* indicate that we are creating commit, not pull request

* update asciinema preview

* nits

admin/prerelease.md

@@ -0,0 +1,27 @@
+# Prereleasing New Version of Docusaurus
+
+[![asciicast](https://asciinema.org/a/hZ7NNJPcgtdvzm5tMLLfHflMD.png)](https://asciinema.org/a/hZ7NNJPcgtdvzm5tMLLfHflMD)
+
+# Steps
+
+1. Ensure that `origin` remote is your Docusaurus fork and `upstream` is Docusaurus original repository. 
+
+```bash
+$ git remote -v
+origin	https://github.com/endiliey/Docusaurus.git (fetch)
+origin	https://github.com/endiliey/Docusaurus.git (push)
+upstream    https://github.com/facebook/Docusaurus.git (fetch)
+upstream    https://github.com/facebook/Docusaurus.git (push)
+```
+
+2. Pull latest changes from Docusaurus repository.
+
+```bash
+$ git fetch upstream && git checkout master && git merge upstream/master
+```
+
+2. Modify `CHANGELOG.md` and other necessary files. Do not commit the changes.
+3. Run `bash scripts/prerelease.sh`.
+4. Create your pull request on GitHub.
+
+<img width="629" alt="pull request" src="https://user-images.githubusercontent.com/17883920/43393765-ccb050ac-942a-11e8-94e8-d585034fa064.PNG">

scripts/prerelease.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+
+DOCS_VERSION_COMMAND="run version"
+
+echo "Select an option for release："
+echo
+
+select VERSION in patch minor major "Specific Version"
+  do
+    echo
+    if [[ $REPLY =~ ^[1-4]$ ]]; then
+      if [[ $REPLY == 4 ]]; then
+        read -p "Enter a specific version: " -r VERSION
+        echo
+        if [[ -z $REPLY ]]; then
+          VERSION=$REPLY
+        fi
+      fi
+
+      read -p "Create $VERSION commit - Are you sure ... (y/n) " -n 1 -r
+      echo
+
+      if [[ $REPLY =~ ^[Yy]$ || -z $REPLY ]]; then
+        # bump version
+        yarn version --new-version $VERSION --no-git-tag-version
+        NEW_VERSION=$(node -p "require('./package.json').version")
+
+        # create new branch
+        git checkout -b $NEW_VERSION master
+
+        # cut docusaurus docs version
+        cd website && yarn $DOCS_VERSION_COMMAND $NEW_VERSION
+        
+        # Create commit
+        git add .
+        git commit -m "v$NEW_VERSION"
+        git push origin $NEW_VERSION
+        echo "Finished"
+      else
+        echo Cancelled
+      fi
+      break
+    else
+      echo Invalid \"${REPLY}\"
+      echo "To continue, please enter one of the options (1-4):"
+      echo
+    fi
+  done