[cantarell-fonts: 10/109] Clarify build instructions

[Nikolaus Waxweiler <nwaxweiler src gnome org>]

commit c1e637b164829651afd7d031a0adb6c6cfae16e1
Author: Nikolaus Waxweiler <madigens gmail com>
Date:   Tue Jul 25 23:40:26 2017 +0200

    Clarify build instructions

 README.md |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/README.md b/README.md
index f4e84a8..493ff6d 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,7 @@ derivative works.
 ```
 pip3 install fontmake --user
 pip3 install -e git+https://github.com/khaledhosny/psautohint#egg=psautohint --user
+# Add both programs to your PATH.
 
 meson build
 cd build