add qldoc to RegExpCharEscape

python/ql/lib/semmle/python/RegexTreeView.qll

@@ -457,6 +457,15 @@ module Impl implements RegexTreeViewSig {
     override string getPrimaryQLClass() { result = "RegExpAlt" }
   }
 
+  /**
+   * A character escape in a regular expression.
+   *
+   * Example:
+   *
+   * ```
+   * \.
+   * ```
+   */
   class RegExpCharEscape = RegExpEscape;
 
   /**