How to Add Notes in Inspector?

I just answered an older question with a much more elegant solution to this problem. I was looking to do the same and didn't like the suggested answers. Checkout my forum post at https://forum.unity3d.com/threads/helpattribute-allows-you-to-use-helpbox-in-the-unity-inspector-window.462768/

You will have to create a custom editor window for your script.

http://docs.unity3d.com/Manual/editor-CustomEditors.html

or you can use a custom property drawer for that...

http://docs.unity3d.com/Manual/editor-PropertyDrawers.html

As a conclusion is not done from the monobehaviour script if that is what you are wondering.

You can follow this example and then improve it for your needs: http://forum.unity3d.com/threads/add-info-text-notes-into-the-inspector.265330/

Also look for the answers to a similar question here: http://answers.unity3d.com/questions/444312/having-text-or-notes-in-the-inspector.html#answer-1111235

If your looking for something permanent for the Inspector like that you could use the code below. I use this method to put notes in my inspector. Just change them whenever you need :)

 [Header("TYPE WHATEVER YOU WANT TO SAY HERE")]