While it’s always free on Steam, you can get it through Square Enix’s website which’ll give you a free key, making this game counts as +1 in your Steam Library so you can get that sweet, sweet Steam Profile XP. 
https://store.na.square-enix-games.com/en_US/product/282531/life-is-strange-episode-1-steam
When I go to activate the key, it says:
“This Steam account already owns the product(s) contained in this offer. To access them, visit your library in the Steam client.”
How do I check to see if it now counts as +1 in my Steam Library? 
It seems you already own the game. This will only work if you didn’t claim it beforehand.
You had to add the key and then check if the counter which tells how many games you have went up.