1. Open package manager
2. Add package from git URL
3. Paste: https://github.com/Motiony/SimpleMinMaxSlider.git#upm (remember the #upm at the end)
4. Let Unity do its thing
5. Done.

Include namespace at the top of your script:

using GD.MinMaxSlider;

Code for the demonstration above:

[MinMaxSlider(0,10)] 
public Vector2 floatTest = new Vector2(2f, 8f);

[MinMaxSlider(0,10)]
public Vector2Int intTest;

Very simple and very handy!