Specify that Map update operator syntax only works for existing keys

[delta1]

Add a note and example that Map update operator only works to update an existing key, and an example to use Map.put/3 for a new key instead.

[doomspork]

@delta1 this is an great addition, thank you and welcome 😁Could you make one small change before we merge this? At the top of the file there is some meta data including the 1.2.5 version. Since we want your changes to be translated let's bump this the version to 1.3.0.

[delta1]

hey @doomspork ! it's a pleasure, thanks for this great resource, the feedback, and the warm welcome :D

I have bumped the version - hope that helps!

[doomspork]

Thank you @delta1 ❤️ both of your PRs were great additions. I hope you'll stick around and continue your awesome contributions.

If you're interested in joining us on Slack you can grab an invite over at http://admissions.elixirschool.com though you may need to give GitHub some time to update (we check for contributions to eliminate spam).

[delta1]

Hey @doomspork you're most welcome, thank you too for the friendly atmosphere and this great project! I don't use slack all that much but I'll try hop on occasionally - and I'll definitely be around to contribute some more :)