[SPARK-33181][SQL][DOCS] Document Load Table Directly from File in SQL Select Reference

### What changes were proposed in this pull request?

Add the link to the feature: "Run SQL on files directly" to SQL reference documentation page

### Why are the changes needed?

To make SQL Reference complete

### Does this PR introduce _any_ user-facing change?

yes. Previously, reading in sql from file directly is not included in the documentation: https://spark.apache.org/docs/latest/sql-ref-syntax-qry-select.html, not listed in from_items. The new link is added to the select statement documentation, like the below:

![image](https://user-images.githubusercontent.com/16770242/96517999-c34f3900-121e-11eb-8d56-c4ba0432855e.png)
![image](https://user-images.githubusercontent.com/16770242/96518808-8126f700-1220-11eb-8c98-fb398eee0330.png)

### How was this patch tested?

Manually built and tested

Closes #30095 from liaoaoyuan97/master.

Authored-by: liaoaoyuan97 <al3468@columbia.edu>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

docs/sql-ref-syntax-qry-select.md

@@ -85,6 +85,7 @@ SELECT [ hints , ... ] [ ALL | DISTINCT ] { named_expression [ , ... ] }
      * [Table-value function](sql-ref-syntax-qry-select-tvf.html)
      * [Inline table](sql-ref-syntax-qry-select-inline-table.html)
      * Subquery
+     * [File](sql-data-sources-load-save-functions.html#run-sql-on-files-directly)
      
 * **PIVOT**