Update the Optuna version and requirements.txt for TPE tutorial

package/samplers/tpe_tutorial/README.md

@@ -3,7 +3,7 @@ author: Shuhei Watanabe
 title: Tree-Structured Parzen Estimator; Understanding Its Algorithm Components and Their Roles for Better Empirical Performance
 description: The optimizer that reproduces the algorithm described in the paper ``Tree-Structured Parzen Estimator; Understanding Its Algorithm Components and Their Roles for Better Empirical Performance''.
 tags: [sampler, tpe, paper, research]
-optuna_versions: [v4.0.0b0]
+optuna_versions: [v4.0.0]
 license: MIT License
 ---
 
@@ -19,6 +19,18 @@ The default parameter set of this sampler is the recommended setup from the pape
 
 - CustomizableTPESampler
 
+## Installation
+
+The version constraint of this package is Optuna v4.0.0 or later.
+
+```shell
+# The requirement is only Optuna.
+$ pip install optuna
+
+# You can also optionally install as follows:
+$ pip install -r https://hub.optuna.org/samplers/tpe_tutorial/requirements.txt
+```
+
 ## Example
 
 This sampler supports the arguments discussed in [the original paper](https://arxiv.org/abs/2304.11127) and can be used in this way.

package/samplers/tpe_tutorial/requirements.txt

@@ -0,0 +1 @@
+optuna>=4.0.0