Add documentation for environment variables.

2 files changed, 3 insertions, 1 deletions

diff --git a/pigz.1 b/pigz.1
index c6a4950..a2f700b 100644
--- a/pigz.1
+++ b/pigz.1
@@ -97,7 +97,9 @@ or
 .PP
 All options on the command line are processed before any names are processed.
 If no names are provided on the command line, or if "-" is given as a name (but
-not after "--"), then the input is taken from stdin.
+not after "--"), then the input is taken from stdin. If the GZIP or PIGZ
+environment variables are set, then options are taken from their values before
+any command line options are processed, first from GZIP, then from PIGZ.
 .PP
 Compressed files can be restored to their original form using
 .I pigz -d
diff --git a/pigz.pdf b/pigz.pdf
index d44da23..cdb11c7 100644
--- a/pigz.pdf
+++ b/pigz.pdf