readme: add tarantoolctl install recipe

We already have recipes how to add the module into dependecies or an
application, but there is no 'just install it' recipe. It is resolved
now.

Fixes #203

Author: Totktonada

README.md

@@ -55,6 +55,13 @@ project:
   tarantool> crud.select('customers', {{'<=', 'age', 35}}, {first = 10})
   tarantool> crud.select('developers', nil, {first = 6})
   ```
+* Install crud into a current directory:
+
+  ```shell
+  $ tarantoolctl rocks install crud
+  ```
+
+  And add the [initialization code](#API) to storage and router instance files.
 * Add crud into dependencies of a Cartridge application and add crud roles into
   dependencies of your roles (see [Cartridge roles](#cartridge-roles) section).
 * Add crud into dependencies of your application (rockspec, RPM spec -- depends