Implement DBSIZE command (#159)

Implement DBSIZE Command - @NicoleStrel

docs/docs/commands/generic/dbsize.mdx

@@ -0,0 +1,47 @@
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+# DBSIZE
+
+### Syntax
+```
+DBSIZE
+```
+
+### Module
+<span className="acl-category">generic</span>
+
+### Categories 
+<span className="acl-category">fast</span>
+<span className="acl-category">read</span>
+<span className="acl-category">keyspace</span>
+
+### Description
+Return the number of keys in the currently-selected database.
+
+### Examples
+
+<Tabs
+  defaultValue="go"
+  values={[
+    { label: 'Go (Embedded)', value: 'go', },
+    { label: 'CLI', value: 'cli', },
+  ]}
+>
+  <TabItem value="go">
+  Get the number of keys in the database:
+  ```go
+  db, err := sugardb.NewSugarDB()
+  if err != nil {
+    log.Fatal(err)
+  }
+  key, err := db.DBSize()
+  ```
+  </TabItem>
+  <TabItem value="cli">
+  Get the number of keys in the database:
+  ```
+  > DBSIZE
+  ```
+  </TabItem>
+</Tabs>