add details on how to change saml button label

doc/integration/saml.md

@@ -38,7 +38,8 @@ First configure SAML 2.0 support in GitLab, then register the GitLab application
                    idp_sso_target_url: 'https://login.example.com/idp',
                    issuer: 'https://gitlab.example.com',
                    name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:transient'
-                 }
+                 },
+          "label" => "Company Login" # optional label for SAML login button, defaults to "Saml"
         }
       ]
     ```
@@ -79,4 +80,4 @@ On the sign in page there should now be a SAML button below the regular sign in
 
 If you see a "500 error" in GitLab when you are redirected back from the SAML sign in page, this likely indicates that GitLab could not get the email address for the SAML user.
 
-Make sure the IdP provides a claim containing the user's email address, using claim name 'email' or 'mail'. The email will be used to automatically generate the GitLab username.
+Make sure the IdP provides a claim containing the user's email address, using claim name 'email' or 'mail'. The email will be used to automatically generate the GitLab username.
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