doc: Add download page (#219)

* doc: Add download page

* Fix links

website/src/download.md

@@ -17,3 +17,45 @@
   ~ under the License.
 -->
 
+# Apache Iceberg™ Rust Downloads
+
+The official Apache Iceberg-Rust releases are provided as source artifacts.
+
+## Releases
+
+The latest source release is [0.2.0](https://www.apache.org/dyn/closer.lua/iceberg/iceberg-rust-0.2.0/apache-iceberg-rust-0.2.0-src.tar.gz?action=download) ([asc](https://downloads.apache.org/iceberg/iceberg-rust-0.2.0/apache-iceberg-rust-0.2.0-src.tar.gz.asc),
+[sha512](https://downloads.apache.org/iceberg/iceberg-rust-0.2.0/apache-iceberg-rust-0.2.0-src.tar.gz.sha512)).
+
+For older releases, please check the [archive](https://archive.apache.org/dist/iceberg/).
+
+## Notes
+
+* When downloading a release, please verify the OpenPGP compatible signature (or failing that, check the SHA-512); these should be fetched from the main Apache site.
+* The KEYS file contains the public keys used for signing release. It is recommended that (when possible) a web of trust is used to confirm the identity of these keys.
+* Please download the [KEYS](https://downloads.apache.org/iceberg/KEYS) as well as the .asc signature files.
+
+### To verify the signature of the release artifact
+
+You will need to download both the release artifact and the .asc signature file for that artifact. Then verify the signature by:
+
+* Download the KEYS file and the .asc signature files for the relevant release artifacts.
+* Import the KEYS file to your GPG keyring:
+
+    ```shell
+    gpg --import KEYS
+    ```
+
+* Verify the signature of the release artifact using the following command:
+
+    ```shell
+    gpg --verify <artifact>.asc <artifact>
+    ```
+
+### To verify the checksum of the release artifact
+
+You will need to download both the release artifact and the .sha512 checksum file for that artifact. Then verify the checksum by:
+
+```shell
+shasum -a 512 -c <artifact>.sha512
+```
+