Rewriting README.md

[MasahikoSawada]

I felt that current README has some out of date information and that chapters seems to be broken. I've started to work on rewriting README.md here. Please give me feedback.

[MasahikoSawada]

PR #50 updates docs.

[harada-toshi]

”3-4. Create pgaudit extension on PostgreSQL server”

• Do you assume postgres as the database name of the installation destination of pgaudit extension?
• When specifying only psql, the target database name becomes environment dependent, so I think that it is better to describe it explicitly.

[harada-toshi]

"Filtering audit log"

As an example of COMMAND_TAG, you probably think that it is better to change the example because I think there is no DDL that displays "CREATE" only.
(If pattern matching is implemented, 'CREATE%' would be a good example)

[harada-toshi]

"Object Audit Logging"

• If the "log_parameter" option is on, the "parameter" column is added to the 9th.
  • In the case of the parameter is not SQL is output <not logged>.
  • In the case of SQL with parameters, parameters are output.

Correction example

Column number	Contents
...	...
9	Parameter. (It is output only when "log_parameter" option is set.)