Add Shell script to import/update rubocop-truffleruby cops

Author: andrykonchin

tool/import-rubocop-truffleruby.sh

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+#!/usr/bin/env bash
+
+# This file should pass `shellcheck tool/import-rubocop-truffleruby.sh`.
+
+set -x
+set -e
+
+SOURCE_DIR="../rubocop-truffleruby"
+SOURCE_PATH="lib/rubocop/cop/truffleruby"
+TARGET_DIR="tool/rubocop-truffleruby"
+GIT_REPO_URL="[email protected]:andrykonchin/rubocop-truffleruby.git"
+
+if [ ! -d "$SOURCE_DIR" ]; then
+  mkdir -p $SOURCE_DIR
+fi
+
+# clone the repository if the SOURCE_DIR is empty
+if [ ! "$(ls $SOURCE_DIR)" ]; then
+  if ! git clone $GIT_REPO_URL $SOURCE_DIR; then
+    echo "FAILURE: git clone failed"
+  fi
+fi
+cp $SOURCE_DIR/$SOURCE_PATH/* $TARGET_DIR/cop/

tool/rubocop-truffleruby/README.md

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+# Rubocop::TruffleRuby
+
+There are some TruffleRuby specific Rubocop copes (a Ruby linter policies) in a `./cop` directory.
+
+They are taken from a `rubocop-truffleruby` gem (https://github.com/andrykonchin/rubocop-truffleruby) and should be synchronized every time the gem is updated.
+
+Use `tool/import-rubocop-truffleruby.sh` Shell script to update them automatically:
+
+```shell
+tool/import-rubocop-truffleruby.sh
+```
+
+The script expects `../rubocop-truffleruby` directory to contain a cloned `rubocop-truffleruby` repository. Otherwise it clones the Git repository itself.