doc: Document that a working environment for building Guix requires "--pure".

* doc/guix.texi (Invoking guix environment): Document that a working
environment for building Guix requires "--pure".

diff --git a/doc/guix.texi b/doc/guix.texi
index b6a9c25..af87d76 100644 (file)
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -4747,7 +4747,7 @@ the following command creates a Guix development environment that
 additionally includes Git and strace:
 
 @example
-guix environment guix --ad-hoc git strace
+guix environment --pure guix --ad-hoc git strace
 @end example
 
 Sometimes it is desirable to isolate the environment as much as