Readme update and improvments

The supplied script, `import_into_DB.sh`, has been designed considering :

* sqlite3 is intalled on the server and executed calling `sqlite3` command (without speciying its path)

* Moodle cron log files are stored in a folder `/var/log/mmodle`

* Moodle cron log files are stored in a folder `/var/log/mmodle`, for example by having a line like this in the server crontab :

  ```

  php -f /path/to/moodle/root/folder/admin/cli/cron.php > /var/log/moodle/cron_$(date +\%H\%M).log 2>&1

  ```

* these files are named `cron_hhmm.log` (for example 'cron_1013.log' is the log file associated with the cron launched at 10h13)

* the shell command `ls -l $f | cut -d ' ' -f 6,7,8` is efficient to extract the file creation date

    * `name` = a name for this kind of error

    * `filtre` = a filtering string that could be used as is, inside a SQL query (with a `LIKE` operator), to get relevant lines

### Queries examples

### Usage

#### SQL clients

To explore results, a SQLite client should be used. Many open source software exist. Such as :

* Command line client, `sqlite3`, itself.  Examples of use :

  ```bash

  sqlite3 moodle-db.logs ".schema task" # to see task's columns

  sqlite3 moodle-db.logs "select count(*) from tasks;"

  ```

* https://sqlitebrowser.org/ a lightweight graphic client

* https://dbeaver.io/ a universal full featured client, able to connect to SQLite dabatase, but also to other types of databases such as mariadb, Oracle, and many others.

#### Queries examples

Below, some examples of what could be done with this database.