Added a way to install additional dependent packages

_sources/installation.rst.txt

@@ -18,3 +18,9 @@ Installation from PYPI
     pip install cshogi
 
 You need pip version 19.0 or higher. If you have a version lower than 19.0, you need to upgrade pip `first <https://pip.pypa.io/en/stable/installing/#upgrading-pip>`_.
+
+If you are using the cshogi.web package, you can install the additional dependencies with the following command:
+
+::
+
+    pip install cshogi[web]

installation.html

@@ -97,6 +97,10 @@ <h2>Installation from PYPI<a class="headerlink" href="#installation-from-pypi" t
 </pre></div>
 </div>
 <p>You need pip version 19.0 or higher. If you have a version lower than 19.0, you need to upgrade pip <a class="reference external" href="https://pip.pypa.io/en/stable/installing/#upgrading-pip">first</a>.</p>
+<p>If you are using the cshogi.web package, you can install the additional dependencies with the following command:</p>
+<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="n">cshogi</span><span class="p">[</span><span class="n">web</span><span class="p">]</span>
+</pre></div>
+</div>
 </section>
 </section>