• Have OSRS downloaded through steam.
  
• Have RuneLite installed from the official website.

1. In your library right-click on OSRS and select properties.
   
2. Disable Steam Overlay and put the path to RuneLite into launch options.

Unless you've changed the path to RuneLite this should be:
For windows users ->

For linux users ->

(obviously replace name with your actual name on your computer)

To have your achievements show on steam:

• Delete the code from launch options.
  
• Launch the game from the steam client and log in.
  
• The achievements you unlocked should pop up.
  
• Close the game and just put the code in launch options again.
  
• Do this everytime you completed an achievement you want to show on your profile.

If encounter an error with the command:

• Make sure you entered the right path to your Runelite.exe (windows) or Runelite.AppImage (linux) file.
  
• If it still doesn't work this is probably because you installed RuneLite in a folder that contains a space.
  
• Just put the path you pasted in launch options in "quotes" to fix this.

You can now have all the benefits of using RuneLite and still have your OSRS play time and achievements show on your steam profile.