Bug 1830847: Update info about upgrade

behatnotneeded

Change-Id: I776133d0e5211e130337c22cf436a4b0b87ce75a
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>

README.md

@@ -33,7 +33,7 @@ The following is a check list of the steps you need to take. Please refer to the
 
 # UPGRADING
 
-Mahara 18.10 supports direct upgrades from previous Mahara versions 15.04.0 and later.
+Mahara 18.10 supports direct upgrades from previous Mahara versions 17.04.0 and later.
 
 If you are upgrading from an earlier version you will need to upgrade
 in either two or three steps:
@@ -50,6 +50,10 @@ then
 
  * Upgrade version 17.04.X -> 'Y'
 
+Note: Older versions of Mahara are not compatible with latest versions
+of PHP so you will need to do intermediate upgrade steps before
+updating your server's PHP
+
 To upgrade an existing Mahara installation, follow the instructions here:
 
  * https://wiki.mahara.org/wiki/System_Administrator%27s_Guide/Upgrading_Mahara