[compat] Add details to blog post excerpt

Author: jnewbery

_posts/en/2019-08-21-compatibility-matrix.md

@@ -8,7 +8,9 @@ lang: en
 slug: 2019-08-21-compatibility-matrix
 
 excerpt: >
-  Announcement of the addition of a new compatibility matrix to the Bitcoin Optech website.
+  Announcing a new compatibility matrix on the Bitcoin Optech website,
+  providing documentation of different wallets' and services' support for scaling
+  technologies.
 
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