Make absolutely sure we're in the right place when executing commands that depend on CWD

Signed-off-by: David Greaves <david.greaves@jollamobile.com>

doc/update/5.0-to-5.1.md

@@ -10,7 +10,7 @@
 ### 2. get latest code
 
 ```
-
+cd /home/git/gitlab
 sudo -u git -H git fetch
 sudo -u git -H git checkout 5-1-stable
 
@@ -27,6 +27,7 @@ sudo -u git -H git checkout v1.3.0
 ### 4. Install libs, migrations etc
 
 ```
+cd /home/git/gitlab
 sudo rm tmp/sockets/gitlab.socket
 sudo -u git -H cp config/puma.rb.example config/puma.rb