[docs] add docs about nightly build

mkdocs/docs/SUMMARY.md

@@ -29,6 +29,7 @@
 - Releases
     - [Verify a release](verify-release.md)
     - [How to release](how-to-release.md)
+    - [Nightly Build](nightly-build.md)
     - [Release Notes](https://github.com/apache/iceberg-python/releases)
 - [Code Reference](reference/)
 

mkdocs/docs/nightly-build.md

@@ -0,0 +1,28 @@
+<!--
+  - Licensed to the Apache Software Foundation (ASF) under one
+  - or more contributor license agreements.  See the NOTICE file
+  - distributed with this work for additional information
+  - regarding copyright ownership.  The ASF licenses this file
+  - to you under the Apache License, Version 2.0 (the
+  - "License"); you may not use this file except in compliance
+  - with the License.  You may obtain a copy of the License at
+  -
+  -   http://www.apache.org/licenses/LICENSE-2.0
+  -
+  - Unless required by applicable law or agreed to in writing,
+  - software distributed under the License is distributed on an
+  - "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  - KIND, either express or implied.  See the License for the
+  - specific language governing permissions and limitations
+  - under the License.
+  -->
+
+# Nightly Build
+
+A nightly build of PyIceberg is available on testpypi, [https://test.pypi.org/project/pyiceberg/](https://test.pypi.org/project/pyiceberg/).
+
+To install the nightly build,
+
+```shell
+pip install -i https://test.pypi.org/simple/ --pre pyiceberg
+```