docs(booleanAttrs): improve parameter docs for boolean attributes

Closes angular#3724

Author: jamesdaily

src/ng/directive/booleanAttrs.js

@@ -165,7 +165,8 @@
     </doc:example>
  *
  * @element INPUT
- * @param {expression} ngDisabled Angular expression that will be evaluated.
+ * @param {expression} ngDisabled If the {@link guide/expression expression} is truthy, 
+ *     then special attribute "disabled" will be set on the element
  */
 
 
@@ -195,7 +196,8 @@
     </doc:example>
  *
  * @element INPUT
- * @param {expression} ngChecked Angular expression that will be evaluated.
+ * @param {expression} ngChecked If the {@link guide/expression expression} is truthy, 
+ *     then special attribute "checked" will be set on the element
  */
 
 
@@ -225,7 +227,8 @@
     </doc:example>
  *
  * @element INPUT
- * @param {string} expression Angular expression that will be evaluated.
+ * @param {expression} ngReadonly If the {@link guide/expression expression} is truthy, 
+ *     then special attribute "readonly" will be set on the element
  */
 
 
@@ -258,7 +261,8 @@
     </doc:example>
  *
  * @element OPTION
- * @param {string} expression Angular expression that will be evaluated.
+ * @param {expression} ngSelected If the {@link guide/expression expression} is truthy, 
+ *     then special attribute "selected" will be set on the element
  */
 
 /**
@@ -290,7 +294,8 @@
      </doc:example>
  *
  * @element DETAILS
- * @param {string} expression Angular expression that will be evaluated.
+ * @param {expression} ngOpen If the {@link guide/expression expression} is truthy, 
+ *     then special attribute "open" will be set on the element
  */
 
 var ngAttributeAliasDirectives = {};