[PATCH 3 of 6] docs: upgrade: make upgrade instructions from version control more explicit

[Thomas De Schampheleire]

# HG changeset patch
# User Thomas De Schampheleire <thomas.de_schampheleire at nokia.com>
# Date 1546033178 -3600
#      Fri Dec 28 22:39:38 2018 +0100
# Node ID 06c1bfe5ca8117733d40dc31a2e6336299bd9683
# Parent  df590100d6ca5fcf6bcf56d90fe5022415f60f16
docs: upgrade: make upgrade instructions from version control more explicit

Instruct users to make a not of the orginal and new revision, both to help
in any failure analysis, and also to let them realize when the 'hg update'
command failed.

diff --git a/docs/upgrade.rst b/docs/upgrade.rst
--- a/docs/upgrade.rst
+++ b/docs/upgrade.rst
@@ -81,10 +81,14 @@ If you originally installed using pip, i
 
     pip install --upgrade kallithea
 
-If you originally installed from version control, it is as simple as::
+If you originally installed from version control, assuming you did not make
+private changes (in which case you should adapt the instructions accordingly)::
 
     cd my-kallithea-clone
-    hg pull -u
+    hg parent   # make a note of the original revision
+    hg pull
+    hg update
+    hg parent   # make a note of the new revision
     pip install --upgrade -e .
     kallithea-cli front-end-build