[Docs] add reference to spaced-comment rule; flesh out options

Author: ljharb

README.md

@@ -1922,7 +1922,7 @@ Other Style Guides
     }
     ```
 
-  - [17.3](#comments--spaces) Start all comments with a space to make it easier to read.
+  - [17.3](#comments--spaces) Start all comments with a space to make it easier to read. eslint: [`spaced-comment`](http://eslint.org/docs/rules/spaced-comment)
 
     ```javascript
     // bad

packages/eslint-config-airbnb-base/rules/style.js

@@ -351,9 +351,18 @@ module.exports = {
     }],
 
     // require or disallow a space immediately following the // or /* in a comment
+    // http://eslint.org/docs/rules/spaced-comment
+    // TODO: semver-major: set balanced to "false"
     'spaced-comment': ['error', 'always', {
-      exceptions: ['-', '+'],
-      markers: ['=', '!']           // space here to support sprockets directives
+      line: {
+        exceptions: ['-', '+'],
+        markers: ['=', '!'], // space here to support sprockets directives
+      },
+      block: {
+        exceptions: ['-', '+'],
+        markers: ['=', '!'], // space here to support sprockets directives
+        balanced: false,
+      }
     }],
 
     // require or disallow the Unicode Byte Order Mark