README.tpm: reflect that vendor_db is in fact logged as "vendor_db"

README.tpm incorrectly stated that  vendor_db is logged as "db"
when in fact it logs as "vendor_db". This caused confusion like

keylime/keylime#1725

Fixing the code risks breaking existing logs, so we're updating
the doc instead. vendor_dbx is in fact logged as "dbx", so that
remains unchanged.

Thanks to Morten Linderud <morten@linderud.pw> for raising this.

Signed-off-by: Jan Setje-Eilers <Jan.SetjeEilers@oracle.com>

Author: jsetje

README.tpm

@@ -13,14 +13,20 @@ PCR7:
   - MokListX - the Mok denylist, logged as "MokListX"
   - vendor_dbx - shim's built-in vendor denylist, logged as "dbx"
   - DB - the system allowlist, logged as "db"
-  - vendor_db - shim's built-in vendor allowlist, logged as "db"
+  - vendor_db - shim's built-in vendor allowlist, logged as "vendor_db"
   - MokList the Mok allowlist, logged as "MokList"
   - vendor_cert - shim's built-in vendor allowlist, logged as "Shim"
   - shim_cert - shim's build-time generated allowlist, logged as "Shim"
 - MokSBState will be extended into PCR7 if it is set, logged as
   "MokSBState".
 - SBAT will be extended into PCR7 if it is set, logged as "SBAT"
 
+Note: In the past this document called out that vendor_db was logged as
+      "db", when in fact the code didn't do that. Since changing the code
+      risks breaking recorded logs, the documentation is update to reflect
+      reality.  vendor_dbx is in fact logged as "dbx".
+
+
 PCR8:
 - If you're using the grub2 TPM patchset we cary in Fedora, the kernel command
   line and all grub commands (including all of grub.cfg that gets run) are