[pitivi] docs: add cd to hacking(meson)

[Thibault Saunier <tsaunier src gnome org>]

commit 4601cc1a5d6d1c1c3a251aa2c5bf4930403c5c40
Author: Henry Wilkes <hwilkes igalia com>
Date:   Thu Oct 17 17:29:57 2019 +0100

    docs: add cd to hacking(meson)
    
    Added the `cd gst-editing-services` command since `setup` is to be run
    in this folder. Also changed the punctuation to make it clearer that
    "Prepare its build directory" is not a separate command, but refers to
    the code block after.

 docs/HACKING.md | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/docs/HACKING.md b/docs/HACKING.md
index aba11c93..8ddea938 100644
--- a/docs/HACKING.md
+++ b/docs/HACKING.md
@@ -123,10 +123,10 @@ which is built using the Meson build system, first clone it into your
 (ptv-flatpak) $ git clone git://anongit.freedesktop.org/gstreamer/gst-editing-services
 ```
 
-Prepare its build directory. Once it has been set up, you won't have to
-run `meson` again for this build directory.
+Prepare its build directory (Once it has been set up, you won't have to
+run `meson` again for this build directory):
 ```
-(ptv-flatpak) $ setup
+(ptv-flatpak) $ cd gst-editing-services && setup
 Using Pitivi prefix in /.../pitivi-dev/pitivi-prefix
 Running in sandbox: meson mesonbuild/ --prefix=/app --libdir=lib -Ddisable_gtkdoc=true -Ddisable_doc=true
 ```