Update docs

docs/docs/index.md

@@ -68,6 +68,15 @@ POETRY_VERSION=0.12.0 python get-poetry.py
 
 ### Alternative installation methods (not recommended)
 
+!!!note
+
+    Using alternative installation methods will make Poetry always
+    use the Python version for which it has been installed to create
+    virtualenvs.
+    
+    So, you will need to install Poetry for each Python version you
+    want to use and switch between them.
+
 #### Installing with `pip`
 
 Using `pip` to install Poetry is possible.