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Copy the URL, then click on the "Insert Link" icon. After you paste the link in the dialog box and press OK, you will notice that part of the link remains highlighted. At that point, simply type in the text you want to "replace" the URL with.
If you miss that, you can just edit the line starting [URL= - you will notice that URL appears twice - the first time in quotes, ending in "], the second occurrence can be replaced with your new text.
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