Add a parameter 'placeholder' to preview.scala.html.

The default value is 'Leave a comment'.

src/main/twirl/preview.scala.html

@@ -1,5 +1,5 @@
 @(repository: service.RepositoryService.RepositoryInfo, content: String, enableWikiLink: Boolean,
-  enableCommitLink: Boolean, enableIssueLink: Boolean, style: String = "")(implicit context: app.Context)
+  enableCommitLink: Boolean, enableIssueLink: Boolean, style: String = "", placeholder: String = "Leave a comment")(implicit context: app.Context)
 @import context._
 <div class="tabbable">
   <ul class="nav nav-tabs">
@@ -12,7 +12,7 @@
   <div class="tab-content">
     <div class="tab-pane active" id="tab1">
       <span id="error-content" class="error"></span>
-      <textarea id="content" name="content"@if(style.nonEmpty){ style="@style"}>@content</textarea>
+      <textarea id="content" name="content"@if(style.nonEmpty){ style="@style"} placeholder="@placeholder">@content</textarea>
     </div>
     <div class="tab-pane" id="tab2">
       <div class="markdown-body" id="preview-area">

src/main/twirl/wiki/wikiedit.scala.html

@@ -21,7 +21,7 @@
   <form action="@path/@repository.owner/@repository.name/wiki/@if(pageName == ""){_new} else {_edit}" method="POST" validate="true">
     <span id="error-pageName" class="error"></span>
     <input type="text" name="pageName" value="@pageName" style="width: 900px; font-weight: bold;" placeholder="Input a page name."/>
-    @html.preview(repository, page.map(_.content).getOrElse(""), true, false, false, "width: 900px; height: 400px;")
+    @html.preview(repository, page.map(_.content).getOrElse(""), true, false, false, "width: 900px; height: 400px;", "")
     <input type="text" name="message" value="" style="width: 900px;" placeholder="Write a small message here explaining this change. (Optional)"/>
     <input type="hidden" name="currentPageName" value="@pageName"/>
     <input type="submit" value="Save" class="btn btn-primary">