Improve Html.toHtml() documentation

The existing documentation is very terse and users were getting
confused whether the method escapes HTML metacharacters or not. Expand
the description a bit and explicitly state that metacharacters are
escaped.

Bug: 17456925

Change-Id: Icaae7fe1344629de5c0860674f3913781de18013

core/java/android/text/Html.java

@@ -137,7 +137,12 @@ public class Html {
     }
 
     /**
-     * Returns an HTML representation of the provided Spanned text.
+     * Returns an HTML representation of the provided Spanned text. A best effort is
+     * made to add HTML tags corresponding to spans. Also note that HTML metacharacters
+     * (such as "<" and "&") within the input text are escaped.
+     *
+     * @param text input text to convert
+     * @return string containing input converted to HTML
      */
     public static String toHtml(Spanned text) {
         StringBuilder out = new StringBuilder();