See python-poetry#4055: mention that the virtual environment poetry i…

…s installed in should not be activated

docs/_index.md

@@ -28,6 +28,7 @@ Poetry should always be installed in a dedicated virtual environment to isolate
 It should in no case be installed in the environment of the project that is to be managed by Poetry.
 This ensures that Poetry's own dependencies will not be accidentally upgraded or uninstalled.
 (Each of the following installation methods ensures that Poetry is installed into an isolated environment.)
+In addition, the isolated virtual environment in which poetry is installed should not be activated for running poetry commands. 
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