Update available prompt

**Is your feature request related to a problem? Please describe.**
Just experienced an issue where because I was on an older version of the IGC cli the commands I was running produced different results to someone else. Upon realising that I needed to update it worked.

**Describe the solution you'd like**
When you run your first command using igc it would prompt to say "did you know version x.x.x is available, would you like to update [y/N]". Idealy it would also suggest how far out of date you are and if the update is recommended.

**Describe alternatives you've considered**
I have tried just updating when I need to but that requires me to remember when I last updated.