swap .sample.env for .env.sample in guide

Author: colinloretz

docs/tutorials/Developing_a_User_Installable_App.mdx

@@ -71,7 +71,7 @@ While we're in your app's settings, we'll want to get a few sensitive values for
 > warn
 > Your token is used to authorize API requests and carry your app's permissions, so they are *highly* sensitive. Make sure to never share your token or check it into any kind of version control.
 
-Back in your project folder, rename the `.sample.env` file to `.env`. `.env` is where we'll store all of your app's credentials.
+Back in your project folder, rename the `.env.sample` file to `.env`. `.env` is where we'll store all of your app's credentials.
 
 We'll need three values from your app's settings for your `.env` file: