Update message to match revised shortcut

[pzaback]

If user attempts to use /edit without any context selected they get a message prompting them to do so. Selection shortcut was recently changed from ctrl/cmd-M to L; this revises the message to match

[netlify[bot]]

✅ Deploy Preview for continuedev canceled.

Name	Link
🔨 Latest commit	fcd27a704266b5108be5db4f3d42987c9cbbb072
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[sestinj]

thank you @pzaback !