Improve clarity of 'dotnet project convert' output directory prompt (#51443)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: jjonescz <[email protected]>

Author: Copilot

src/Cli/dotnet/Commands/CliCommandStrings.resx

@@ -1533,7 +1533,7 @@ Tool '{1}' (version '{2}') was successfully installed. Entry is added to the man
     <value>Convert a file-based program to a project-based program.</value>
   </data>
   <data name="ProjectConvertAskForOutputDirectory" xml:space="preserve">
-    <value>Specify the output directory ({0}):</value>
+    <value>Specify the output directory (press Enter for default: '{0}', directory must not exist):</value>
     <comment>{0} is the default value</comment>
   </data>
   <data name="ProjectConvertDryRun" xml:space="preserve">