pgvector: add release notes for 0.8.1 and 0.8.2

The page for 0.8.1 was missing, and the page for 0.8.2 is to cover the
new release that fixes a CVE.

Author: tureba

advocacy_docs/pg_extensions/pgvector/rel_notes/index.mdx

@@ -6,4 +6,6 @@ The `pgvector` documentation describes the latest version of `pgvector`, includi
 
 |               Version               | Release Date |
 | ----------------------------------- | ------------ |
+| [0.8.2](pgvector_0.8.2_rel_notes) | 27 Feb 2026  |
+| [0.8.1](pgvector_0.8.1_rel_notes) | 04 Nov 2025  |
 | [0.8.0](pgvector_0.8.0_rel_notes) | 30 Oct 2024  |

advocacy_docs/pg_extensions/pgvector/rel_notes/pgvector_0.8.1_rel_notes.mdx

@@ -0,0 +1,11 @@
+---
+title: Release notes for pgvector
+navTitle: "Version 0.8.1"
+---
+
+In addition to the [pgvector 0.8.1 changes](https://github.com/pgvector/pgvector/blob/master/CHANGELOG.md#081-2025-09-04), this release also includes:
+
+|  Type   |                                              Description                                              |
+| ------- | ----------------------------------------------------------------------------------------------------- |
+| Feature | Added support for PostgreSQL 18, EDB Postgres Extended Server 18, and EDB Postgres Advanced Server 18 |
+

advocacy_docs/pg_extensions/pgvector/rel_notes/pgvector_0.8.2_rel_notes.mdx

@@ -0,0 +1,10 @@
+---
+title: Release notes for pgvector
+navTitle: "Version 0.8.2"
+---
+
+In addition to the [pgvector 0.8.2 changes](https://github.com/pgvector/pgvector/blob/master/CHANGELOG.md#082-2026-02-25), this release also includes:
+
+|   Type   |                             Description                                  |
+| -------- | ------------------------------------------------------------------------ |
+| Security | Fixes [CVE-2026-3172](https://github.com/advisories/GHSA-789c-mgqf-5hwx) |