python-utils-r1.eclass: python_moduleinto, clarify relative path use

Clearly indicate that python_moduleinto can be safely called outside
of the environment with Python interpreter established, and that
a single call can set the correct relative path for multiple different
implementations.

eclass/python-utils-r1.eclass

@@ -815,6 +815,12 @@ python_newscript() {
 # When not set explicitly, the modules are installed to the top
 # site-packages directory.
 #
+# In the relative case, the exact path is determined directly
+# by each python_doscript/python_newscript function. Therefore,
+# python_moduleinto can be safely called before establishing the Python
+# interpreter and/or a single call can be used to set the path correctly
+# for multiple implementations, as can be seen in the following example.
+#
 # Example:
 # @CODE
 # src_install() {