Update Okta instructions

I recently verified that the comments in
https://bugs.chromium.org/p/gerrit/issues/detail?id=12570
are applicable and resolve the errors that will occur if the current
instructions are followed.

The serviceProviderEntityId setting described in the issue does not
appear to be required.

Change-Id: Iea252cfccab505a87b76185c00e3acdd47cdc4ec

okta/README.md

diff --git a/okta/README.md b/okta/README.md
index 4d67ba9..45bf0e5 100644
--- a/okta/README.md
+++ b/okta/README.md
@@ -2,7 +2,7 @@
 
 - Create a new SAML 2.0 application.
 - Set the following parameters:
-  - Single sign on URL: http://gerrit.site.com/plugins/saml/callback
+  - Single sign on URL: http://gerrit.site.com/plugins/saml/callback?client_name=SAML2Client
   - Check "Use this for Recipient URL and Destination URL".
   - Audience URI (SP Entity Id): http://gerrit.site.com/plugins/saml/callback
   - We need to set up the attributes in the assertion to send the right
@@ -17,4 +17,4 @@
       do not do so, the name will be taken from the NameId provided by
       the assertion.  This is why in Okta we set the application username to
       "Okta username prefix".
-- Obtain your IdP metadata (either URL or a local XML file)
\ No newline at end of file
+- Obtain your IdP metadata (either URL or a local XML file)