Add new tool to build gem

tools/gem.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+#
+# Create a ruby-gem pakcage with doc
+#
+# Required: rubygem, yard
+
+set -eu
+
+GEM_CONFIG="./jekyll-theme-chirpy.gemspec"
+
+if [[ ! -f $GEM_CONFIG ]]; then
+  echo "Error: .gemspec file not found!"
+  exit -1
+fi
+
+if [[ -d doc ]]; then
+  rm -rf doc
+fi
+
+yard doc
+
+gem build "$GEM_CONFIG"