Automatically create a ~/.gemrc file

* To avoid generating documentation on `gem install`, which can take a long time.

index.js

@@ -18,6 +18,8 @@ export async function run() {
     const engineVersions = installer.getAvailableVersions(platform, engine)
     const ruby = validateRubyEngineAndVersion(platform, engineVersions, engine, version)
 
+    createGemRC()
+
     const [rubyPrefix, newPathEntries] = await installer.install(platform, ruby)
 
     setupPath(ruby, newPathEntries)
@@ -82,6 +84,13 @@ function validateRubyEngineAndVersion(platform, engineVersions, engine, version)
   return engine + '-' + version
 }
 
+function createGemRC() {
+  const gemrc = path.join(os.homedir(), '.gemrc')
+  if (!fs.existsSync(gemrc)) {
+    fs.writeFileSync(gemrc, `gem: --no-document${os.EOL}`)
+  }
+}
+
 function setupPath(ruby, newPathEntries) {
     const originalPath = process.env['PATH'].split(path.delimiter)
     let cleanPath = originalPath.filter(entry => !/\bruby\b/i.test(entry))