[docs] Update "how to release" doc (#1700)

Updating the docs as we learn from the 0.9.0 release.

Doc improvements:
* Updating `KEYS` file requires PMC access. 

Rendered locally:

<img width="777" height="192" alt="Screenshot 2025-10-26 at 2 40 50 PM"
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Co-authored-by: Fokko Driesprong <[email protected]>

Author: kevinjqliu

mkdocs/docs/how-to-release.md

@@ -30,6 +30,7 @@ This guide outlines the process for releasing PyIceberg in accordance with the [
 ## Requirements
 
 * A GPG key must be registered and published in the [Apache Iceberg KEYS file](https://downloads.apache.org/iceberg/KEYS). Follow [the instructions for setting up a GPG key and uploading it to the KEYS file](#set-up-gpg-key-and-upload-to-apache-iceberg-keys-file).
+    * Permission to update the `KEYS` artifact in the [Apache release distribution](https://dist.apache.org/repos/dist/release/iceberg/) (requires Iceberg PMC privileges).
 * SVN Access
     * Permission to upload artifacts to the [Apache development distribution](https://dist.apache.org/repos/dist/dev/iceberg/) (requires Apache Committer access).
     * Permission to upload artifacts to the [Apache release distribution](https://dist.apache.org/repos/dist/release/iceberg/) (requires Apache PMC access).
@@ -405,5 +406,12 @@ cd icebergsvn
 echo "" >> KEYS # append a newline
 gpg --list-sigs <YOUR KEY ID HERE> >> KEYS # append signatures
 gpg --armor --export <YOUR KEY ID HERE> >> KEYS # append public key block
-svn commit -m "add key for <YOUR NAME HERE>"
+svn commit -m "add key for <YOUR NAME HERE>" # this requires Iceberg PMC privileges
 ```
+
+<!-- prettier-ignore-start -->
+
+!!! note
+    Updating the `KEYS` artifact in the `release/` distribution requires Iceberg PMC privileges. Please work with a PMC member to update the file.
+
+<!-- prettier-ignore-end -->