[SPARK-28828][DOC] Document REFRESH TABLE command

### What changes were proposed in this pull request?
Document REFRESH TABLE statement in the SQL Reference Guide.

### Why are the changes needed?
Currently there is no documentation in the SPARK SQL to describe how to use this command, it is to address this issue.

### Does this PR introduce any user-facing change?
Yes.
#### Before:
There is no documentation for this.

#### After:
<img width="826" alt="Screen Shot 2019-09-12 at 11 39 21 AM" src="https://user-images.githubusercontent.com/7550280/64811385-01752600-d552-11e9-876d-91ebb005b851.png">

### How was this patch tested?
Using jykll build --serve

Closes #25549 from kevinyu98/spark-28828-refreshTable.

Authored-by: Kevin Yu <qyu@us.ibm.com>
Signed-off-by: Xiao Li <gatorsmile@gmail.com>

docs/_data/menu-sql.yaml

@@ -172,6 +172,8 @@
                   url: sql-ref-syntax-aux-cache-uncache-table.html
                 - text: CLEAR CACHE
                   url: sql-ref-syntax-aux-cache-clear-cache.html
+                - text: REFRESH TABLE
+                  url: sql-ref-syntax-aux-refresh-table.html
             - text: Describe Commands
               url: sql-ref-syntax-aux-describe.html
               subitems:

docs/sql-ref-syntax-aux-refresh-table.md

@@ -0,0 +1,58 @@
+---
+layout: global
+title: REFRESH TABLE
+displayTitle: REFRESH TABLE
+license: |
+  Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to You under the Apache License, Version 2.0
+  (the "License"); you may not use this file except in compliance with
+  the License.  You may obtain a copy of the License at
+ 
+     http://www.apache.org/licenses/LICENSE-2.0
+ 
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+---
+
+### Description
+`REFRESH TABLE` statement invalidates the cached entries, which include data
+and metadata of the given table or view. The invalidated cache is populated in
+lazy manner when the cached table or the query associated with it is executed again.
+
+### Syntax
+{% highlight sql %}
+REFRESH [TABLE] tableIdentifier
+{% endhighlight %}
+
+### Parameters
+<dl>
+  <dt><code><em>tableIdentifier</em></code></dt>
+  <dd>
+    Specifies a table name, which is either a qualified or unqualified name that designates a table/view. If no database identifier is provided, it refers to a temporary view or a table/view in the current database.<br><br>
+    <b>Syntax:</b>
+      <code>
+        [database_name.]table_name
+      </code>
+  </dd>
+</dl>
+
+### Examples
+{% highlight sql %}
+-- The cached entries of the table will be refreshed  
+-- The table is resolved from the current database as the table name is unqualified.
+REFRESH TABLE tbl1;
+
+-- The cached entries of the view will be refreshed or invalidated
+-- The view is resolved from tempDB database, as the view name is qualified.
+REFRESH TABLE tempDB.view1;   
+{% endhighlight %}
+
+### Related Statements
+- [CACHE TABLE](sql-ref-syntax-aux-cache-cache-table.html)
+- [CLEAR CACHE](sql-ref-syntax-aux-cache-clear-cache.html)
+- [UNCACHE TABLE](sql-ref-syntax-aux-cache-uncache-table.html)