bpo-33456: site module documentation - fix wrong default for key in pyvenv.cfg (GH-6755)

Doc/library/site.rst

@@ -45,9 +45,9 @@ sys.prefix and sys.exec_prefix are set to that directory and
 it is also checked for site-packages (sys.base_prefix and
 sys.base_exec_prefix will always be the "real" prefixes of the Python
 installation). If "pyvenv.cfg" (a bootstrap configuration file) contains
-the key "include-system-site-packages" set to anything other than "false"
-(case-insensitive), the system-level prefixes will still also be
-searched for site-packages; otherwise they won't.
+the key "include-system-site-packages" set to anything other than "true"
+(case-insensitive), the system-level prefixes will not be
+searched for site-packages; otherwise they will.
 
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