[epiphany] Instructions for running valgrind lack 'valgrind'

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 93bc6843e4bf7a26eea3dc1eb1724d20ea99da18
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Sun Jan 12 18:46:46 2020 +0000

    Instructions for running valgrind lack 'valgrind'
    
    valgrind works better when not missing from the command line.

 HACKING.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/HACKING.md b/HACKING.md
index b634a003c..07a72752e 100644
--- a/HACKING.md
+++ b/HACKING.md
@@ -215,5 +215,5 @@ To use valgrind, you must use environment variables to disable WebKit's sandbox
 and JavaScriptCore's Gigacage:
 
 ```
-WEBKIT_FORCE_SANDBOX=0 GIGACAGE_ENABLED=0 G_SLICE=always-malloc epiphany
+WEBKIT_FORCE_SANDBOX=0 GIGACAGE_ENABLED=0 G_SLICE=always-malloc valgrind epiphany
 ```