[pitivi] Fix error message in git hook

[Alexandru Băluț <alexbalut src gnome org>]

commit e32b513599bbf11b642b492d6d6fe60be5ab99f1
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Mon Nov 4 21:53:06 2019 +0100

    Fix error message in git hook

 pre-commit.hook | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
---
diff --git a/pre-commit.hook b/pre-commit.hook
index 44cae3bb..c605a319 100755
--- a/pre-commit.hook
+++ b/pre-commit.hook
@@ -4,7 +4,13 @@
 # the dev env with `source bin/pitivi-env`.
 
 if [ -z "${PITIVI_REPO_DIR}" ]; then
-    echo "ERROR: You're not in the Pitivi development environment. Run `source bin/pitivi-env` to enter it. 
See http://developer.pitivi.org/HACKING.html for details."
+    echo "ERROR: You're not in the Pitivi development environment."
+    echo
+    echo "       Enter the development environment by running:"
+    echo "           $ . bin/pitivi/env"
+    echo
+    echo "       See http://developer.pitivi.org/HACKING.html for details."
+    echo
     exit 1
 fi