Added wording to description of Buddhist calendar alluding to the calendar reform of 1940

Author: ben-allen

spec.emu

@@ -54,7 +54,7 @@ contributors: Google, Ecma International
           </thead>
           <tr>
             <td>*"buddhist"*</td>
-            <td>Thai Buddhist calendar, proleptic. Month numbers, month codes, and days are the same as in the ISO 8601 calendar, but the epoch year is different. There is one era.</td>
+            <td>Thai Buddhist calendar, proleptic. Month numbers, month codes, and days are identical to ISO 8601 starting on 1 January 1941, but the epoch year is different. Earlier dates are implementation-defined due to the calendar reform of 1940. There is one era.</td>
           </tr>
           <tr>
             <td>*"chinese"*</td>