docs: add some information about metadata signing (simplesamlphp#2461)

* docs: add some information about metadata signing

Link to the relevant section in both SP and IdP hosting sections of
the docs.

* linto

Author: monkeyiq

docs/simplesamlphp-reference-idp-hosted.md

@@ -35,6 +35,11 @@ select the correct configuration. One entry in the metadata-list can
 have the host `__DEFAULT__`. This entry will be used when no other
 entry matches.
 
+Directives that relate to signing of metadata start with the
+`metadata.sign` prefix. The signing directives are documented in their
+[own section](simplesamlphp-advancedfeatures.html#metadata-signing).
+in the advanced features page.
+
 ## Common options
 
 `auth`

modules/saml/docs/sp.md

@@ -4,6 +4,11 @@ This authentication source is used to authenticate against SAML 2 IdPs.
 
 ## Metadata
 
+Directives that relate to signing of metadata start with the
+`metadata.sign` prefix. The signing directives are documented in their
+[own section](simplesamlphp-advancedfeatures.html#metadata-signing).
+in the advanced features page.
+
 The metadata for your SP will be available from the federation page on your SimpleSAMLphp installation.
 
 SimpleSAMLphp supports generating metadata with the MDUI and MDRPI metadata extensions