wrong filter wpsimplesaml_idp_metadata_xml in documentation

[yanmorinokamca]

In https://github.com/humanmade/wp-simple-saml/wiki/Testing-SSO-locally
wpsimplesaml_idp_metadata_xml filter should be wpsimplesaml_idp_metadata_xml_path

[yanmorinokamca]

also, in the docker run:
-e SIMPLESAMLPHP_SP_ENTITY_ID=http://mysite.local \
the entity_id should be compatible with the metadata id (sso_sp_base) which has a '/' by default in get_sso_settings()

sso_sp_base' => is_sso_enabled_network_wide() ? get_home_url( get_network()->site_id, '/' ) : home_url( '/' )

it's working better with: -e SIMPLESAMLPHP_SP_ENTITY_ID=http://mysite.local/ \

Otherwise you get a Unable to locate metadata for 'https://mysite.local/' when testing the authentification.