readme: on some systems no .zip suffix
diff --git a/README.md b/README.md
index f5543b0..4a67d7f 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,7 @@
```bash
$ cd ~
$ wget https://github.com/pagespeed/ngx_pagespeed/archive/release-1.5.27.2-beta.zip
- $ unzip release-1.5.27.2-beta.zip
+ $ unzip release-1.5.27.2-beta.zip # or unzip release-1.5.27.2-beta
$ cd ngx_pagespeed-release-1.5.27.2-beta/
$ wget https://dl.google.com/dl/page-speed/psol/1.5.27.2.tar.gz
$ tar -xzvf 1.5.27.2.tar.gz # expands to psol/