Added some missing syntax highlighting for descriptions.

core/src/main/resources/hudson/model/Job/configure.jelly

@@ -41,7 +41,7 @@ THE SOFTWARE.
           </f:entry>
         </j:if>
         <f:entry title="${%Description}" help="${app.markupFormatter.helpUrl}">
-          <f:textarea name="description" value="${it.description}"/>
+          <f:textarea name="description" value="${it.description}" codemirror-mode="htmlmixed" codemirror-config="mode:'text/html'"/>
         </f:entry>
 
         <j:if test="${it.supportsLogRotator()}">

core/src/main/resources/hudson/model/Run/configure.jelly

@@ -33,7 +33,7 @@ THE SOFTWARE.
           <f:textbox name="displayName" value="${it.hasCustomDisplayName()?it.displayName:''}"/>
         </f:entry>
         <f:entry title="${%Description}" help="/help/run-config/description.html">
-          <f:textarea name="description" value="${it.description}"/>
+          <f:textarea name="description" value="${it.description}" codemirror-mode="htmlmixed" codemirror-config="mode:'text/html'"/>
         </f:entry>
 
         <j:if test="${h.hasPermission(it,it.UPDATE)}">