Click the little Earth looking icon "Insert Link" in the reply box then paste the link into that pop up and click ok. Now the entire URL can be clicked, you can then edit part of it (like removing the www. and the .com) so just the word shows but it's still a click-able link. This is how I do it at least.
You can even type an entire new word inside the link then remove everything but that word and it will still be a link.
Example you posted "www.monsterfishkeepers.com"
Then you did this "www.monsterCLICKfishkeepers.com"
Then you erased all but the click so it just shows "CLICK"
Now when you click the "CLICK" it will link to MFK.
Note these are NOT real links, just examples.