Add `CREATE VIEW` documentation to user guide

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
In docs/source/user-guide/sql/ddl.md we do not show that we support CREATE VIEW.

Describe the solution you'd like
Add docs

Describe alternatives you've considered
None

Additional context
None

[madihabdul]

Hi, I could take on this issue!

[alamb]

Thanks @madihabdul !

[kmitchener]

@madihabdul do you need some assistance with this issue? I'd be happy to help

[alamb]

@madihabdul do you need some assistance with this issue? I'd be happy to help

@kmitchener given there is no PR up if you don't hear from @madihabdul I would recommend just proceeding. Thank you for checking first.

[retikulum]

Hi. As this issue is not closed or proceed, I will suggest following explanation for it. Is it enough?

CREATE VIEW

View is a virtual table based on the result of a SQL query. It can be created from an existing table or values list

CREATE VIEW view_name AS statement;

CREATE TABLE users AS VALUES(1,2),(2,3),(3,4),(4,5);
CREATE VIEW test AS SELECT column1 FROM users;
SELECT * FROM test;
+---------+
| column1 |
+---------+
| 1       |
| 2       |
| 3       |
| 4       |
+---------+

CREATE VIEW test AS VALUES(1,2),(5,6);
SELECT * FROM test;
+---------+---------+
| column1 | column2 |
+---------+---------+
| 1       | 2       |
| 5       | 6       |
+---------+---------+

[alamb]

Thanks @retikulum -- your proposal looks great to me. We can always add some documentation and then expand upon it in future PRs

[retikulum]

I hope I will contribute datafusion more as I get used to codebase