Minor upgrade guide text change

UPGRADE-2.0.md

@@ -1,8 +1,8 @@
-# Upgrades guides for Composer 1.x to 2.0
+# Upgrade guides for Composer 1.x to 2.0
 
 ## For composer CLI users
 
-- Packages existing in a higher priority repository will now be entirely ignored from lower repository ones
+- If a packages exists in a higher priority repository, it will now be entirely ignored in lower repository ones
 - Invalid PSR-0 / PSR-4 class configurations will not autoload anymore in optimized-autoloader mode, as per the warnings introduced in 1.10
 - Package names now must comply to our naming guidelines or Composer will abort, as per the warnings introduced in 1.8.1
 - Removed --no-suggest flag as it is not needed anymore