Guide about date

According to

```
9. [Mandatory] A table must include three columns as following: id, gmt_create and gmt_modified.

Note: id is the primary key, which is unsigned bigint and self-incrementing with step length of 1. The type of gmt_create and gmt_modified should be DATETIME.

```

Can I understand that in Alibaba it is recommended to define the date type as DATETIME? If not, shall we add guide about this? TIMESTAMP or DATETIME is the right choice?

We see that it is mandatory to define gmt_create, gmt_modified, can we understand that when dealing with cross time zone issues you recommend storing the date of gmt time in the database and then converting it to local time zone for display?

Nell’issue non sono identificati né un file né un test. Determina innanzitutto se la guida debba raccomandare DATETIME o TIMESTAMP e come debbano essere gestiti i valori UTC tra i fusi orari; il lavoro sarà completato quando la linea guida conterrà una raccomandazione inequivocabile e indicazioni sui fusi orari.

Scritto dal modello di indicizzazione a partire dal testo della issue.