docs: link FIPS page from the Percona comparison

Now that the FIPS compliance page is on main, restore the link that was left as
plain text while the FIPS change was in a separate PR.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: OffgridwithJD

documentation/docs/index/comparison-percona.md

@@ -53,7 +53,7 @@ Beyond running on upstream PostgreSQL, this fork has added:
   [`open_pg_tde.data_cipher`](../variables.md#open_pg_tdedata_cipher).
 - **FIPS enforcement.** All cryptography runs through OpenSSL and uses
   FIPS-approved modes, and the server can be required to start only when OpenSSL
-  is in FIPS mode.
+  is in FIPS mode. See [FIPS compliance](fips.md).
 - **A documented threat model** stating what encryption at rest does and does not
   protect. See the [threat model](threat-model.md).