Add columnstore variables to README

Author: miguilimzero

README.md

@@ -195,6 +195,22 @@ Schema::create('table', function (Blueprint $table) {
 
 ```
 
+### Sort Keys - Columnstore variables
+
+Sometimes you may want to customize your [columstore variables](https://docs.singlestore.com/managed-service/en/create-a-database/physical-database-schema-design/procedures-for-physical-database-schema-design/configuring-the-columnstore-to-work-effectively.html) individually per table. You can do it by appending `with` fluently to the `sortKey` definition.
+
+```php
+Schema::create('table', function (Blueprint $table) {
+    $table->string('name');
+
+    $table->sortKey('name')->with(['columnstore_segment_rows' => 100000]);
+});
+
+Schema::create('table', function (Blueprint $table) {
+    $table->string('name')->sortKey()->with(['columnstore_segment_rows' => 100000]);
+});
+```
+
 ### Series Timestamps
 To denote a column as a series timestamp, use the `seriesTimestamp` column modifier.