docs: add user guide

Author: kenjis

user_guide_src/source/changelogs/v4.4.0.rst

@@ -61,6 +61,7 @@ Others
 
 - **MySQLi:** Added the ``numberNative`` attribute to the Database Config to keep the variable type obtained after SQL Query consistent with the type set in the database.
   See :ref:`Database Configuration <database-configuration-explanation-of-values>`.
+- **SQLSRV:** Field Metadata now includes ``nullable``. See :ref:`db-metadata-getfielddata`.
 
 Model
 =====

user_guide_src/source/database/metadata.rst

@@ -78,6 +78,8 @@ performing an action. Returns a boolean true/false. Usage example:
 Retrieve Field Metadata
 =======================
 
+.. _db-metadata-getfielddata:
+
 $db->getFieldData()
 -------------------
 
@@ -104,9 +106,11 @@ database:
 -  type - the type of the column
 -  max_length - maximum length of the column
 -  primary_key - integer ``1`` if the column is a primary key (all integer ``1``, even if there are multiple primary keys), otherwise integer ``0`` (This field is currently only available for MySQL and SQLite3)
--  nullable - boolean ``true`` if the column is nullable, otherwise boolean ``false`` (This field is currently not available in SQL Server)
+-  nullable - boolean ``true`` if the column is nullable, otherwise boolean ``false``
 -  default - the default value
 
+.. note:: Since v4.4.0, SQLSRV supported ``nullable``.
+
 List the Indexes in a Table
 ===========================