added more details and security-policy sample config

[aprabh92]

Additional details added to detailed readme file and sample config for security policy

[aprabh92]

added ipsec example

[aprabh92]

Hello @davedotdev made the respective changes

• changes based on comments provided
• modified earlier ipsec files with the ones you helped following best practices
• added l3vpn sample configuration

[aburston]

This has been included in https://github.com/Juniper/junos-terraform/pull/45.

So closing.