Clarified info about default disabled link schemas

lib/index.js

@@ -273,8 +273,10 @@ function MarkdownIt(presetName, options) {
    * MarkdownIt#validateLink(url) -> Boolean
    *
    * Link validation function. CommonMark allows too much in links. By default
-   * we disable `javascript:` and `vbscript:` schemas. You can change this
-   * behaviour.
+   * we disable `javascript:`, `vbscript:`, `file:` schemas, and almost all `data:...` schemas
+   * except some embedded image types.
+   * 
+   * You can change this behaviour:
    *
    * ```javascript
    * var md = require('markdown-it')();