ORM tutorial mentions read, insert and delete, but not update

[Tom Tom]

The tutorial at http://docs.sqlalchemy.org/en/rel_0_9/orm/tutorial.html explains how to a read, insert and delete query, but it doesn't explain how to update.

I think it would be very helpful to the new user of SQLAlchemy if the tutorial explains this.

[Mike Bayer]

• clarify the "Adding" section also illustrates updates, fixes #2942

→ <<cset 02271efd8976>>

[Mike Bayer]

• clarify the "Adding" section also illustrates updates, fixes #2942

(cherry picked from commit 02271efd8976154f855646478b5438db078f7101)

→ <<cset b425fd8eda88>>

[Mike Bayer]

• clarify the "Adding" section also illustrates updates, fixes #2942

(cherry picked from commit 02271efd8976154f855646478b5438db078f7101)

→ <<cset 9588b6b244f3>>