docs(model/attributes): add docs for attribute.field

lib/sequelize.js

@@ -285,6 +285,7 @@ module.exports = (function() {
    *             msg: "Must be English or Chinese"
    *           }
    *         },
+   *         field: 'column_a'
    *         // Other attributes here
    *     },
    *     columnB: Sequelize.STRING,
@@ -312,6 +313,7 @@ module.exports = (function() {
    * @param {Any}                     [attributes.column.defaultValue=null] A literal default value, a javascript function, or an SQL function (see `sequelize.fn`)
    * @param {String|Boolean}          [attributes.column.unique=false] If true, the column will get a unique constraint. If a string is provided, the column will be part of a composite unique index. If multiple columns have the same string, they will be part of the same unique index
    * @param {Boolean}                 [attributes.column.primaryKey=false]
+   * @param {String}                  [attributes.column.field=null] If set, sequelize will map the attribute name to a different name in the database
    * @param {Boolean}                 [attributes.column.autoIncrement=false]
    * @param {String}                  [attributes.column.comment=null]
    * @param {String|Model}            [attributes.column.references] If this column references another table, provide it here as a Model, or a string