Updated documentation to make mention of memcached caveats

Signed-off-by: Dhruv Govil <[email protected]>

src/rez/rezconfig.py

@@ -500,9 +500,15 @@
 allow_unversioned_packages = True
 
 # Defines whether a resolve should immediately fail if any variants have a required package that can't be found.
-# It is enabled by default.
+# This can be useful to disable if you have packages that aren't available to all users.
+# It is enabled by default. If a variant has requires that cannot be found , it will error immediately rather than
+# trying the other variants.
 # If disabled, it will try other variants before giving up.
-# This can be useful if you have variants that aren't available to all users.
+#
+# .. warning::
+#    Memcached isn't tested with scenarios where you expect users to have access to different sets of packages.
+#    It expects that every user can access the same set of packages, which may cause incorrect resolves
+#    when this option is disabled.
 error_on_missing_variant_requires = True
 
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