update README for SQLite

[yangoon1, 2010-02-26 12:15:08]

http://codereview.appspot.com/223064/diff/1/2
File README (right):

http://codereview.appspot.com/223064/diff/1/2#newcode34
README:34: -----------------
Database Backends (RDBMS)
-------------------------

http://codereview.appspot.com/223064/diff/1/2#newcode37
README:37: available. Here is some warnings about using other backends:
Tryton uses a RDBMS (Relational Database Management System) as backend. It is
mainly developed for PostgreSQL, but there are connectors to other backends
available.

Some considerations about the use of other backends:

http://codereview.appspot.com/223064/diff/1/2#newcode54
README:54: * SQLite can not alter column definition nor create foreign key.
SQLite can not alter column definitions nor create foreign keys.

http://codereview.appspot.com/223064/diff/1/2#newcode56
README:56: * SQL constraints are validate by Tryton instead of database.
SQL constraints are validated by Tryton instead of the DBMS.

[yangoon1, 2010-02-26 15:03:40]

http://codereview.appspot.com/223064/diff/1002/6
File README (right):

http://codereview.appspot.com/223064/diff/1002/6#newcode56
README:56: * SQL constraints are validated by Tryton instead of database.
instead of database.

Not ok for me, since the DBMS validates. This was the cause for my proposal.