CREATE TABLE Doc Update

[bdarnell]

Re: CREATE TABLE

Issue Description

The first example creates a table with no primary key, but this is never desirable in CRDB.

Suggested Resolution

Swap the order of the with/without primary key examples. Add a warning to the "no primary key" example indicating that this is supported for compatibility with other databases, but that it's always better to specify a primary key.

[ericharmeling]

Resolving this as a part of this PR: #5075

Will reference this issue in that PR.