edit ch8 adding metadata

book/source/08-signing_components.md

@@ -142,20 +142,20 @@ Linking a User ID to an OpenPGP certificate
 (primary-metadata)=
 ### Adding metadata to the primary key/certificate
 
-The signatures that bind subkeys and identity components to a certificate serve two different purposes: Linking components to the certificate and adding metadata to a component.
+The signatures that bind subkeys and identity components to a certificate serve dual purposes: linking components to the certificate and adding metadata to components.
 
-The primary key in a certificate doesn't need to be linked to the certificate. It acts as the anchor for linking, itself and thus doesn't require being linked. However, there is nevertheless a need to associate metadata with the primary key, which typically applies to the certificate as a whole.
+Unlike these components, the primary key of a certificate doesn't require a linking signature since it serves as the central anchor of the certificate. However, associating metadata with the primary key is still essential, as it generally applies to the entire certificate.
 
-There are two mechanisms for adding metadata to the primary key:
+Metadata can be added to the primary key via two mechanisms:
 
-- Via a direct key signature on the primary key, or
-- via a "primary User ID" binding signature.
+- direct key signature on the primary key
+- *primary User ID* binding signature
 
-Relevant metadata for the primary key that is defined the above mechanisms includes:
+The types of metadata typically associated with the primary key through these methods include:
 
-- Key expiration,
-- key flags,
-- algorithm preference signaling.
+- key expiration
+- key flags
+- algorithm preference signaling
 
 (direct_key_signature)=
 #### Direct key signature