Null check, better violation msgs, and added function descriptions

[ja5onhughe5]

• Created better violation messages
• Added a null check for aws_security_group_rule loop
• Updated test mocks for the null check
• Cleaned up the loop for aws_security_group
• Added function descriptions for tfplan docs

[rberlind]

Looks good, @ja5onhughe5 . Thanks for adding the new MD files.
One note: you don't need to add extra spaces and end of strings given in double quotes in the print() function when combining multiple with commas. For instance, `print("Roger", "Berlind") will print "Roger Berlind" since the print() function adds a space. But you don't have to change what you have.