fix typo: usefull -> useful

docs/build/html/build-the-docs.html

@@ -210,7 +210,7 @@ <h2>Generating documentation from docstrings<a class="headerlink" href="#generat
 Creating file ./source/modules.rst.
 </pre></div>
 </div>
-<p>The above command generates two files: <code class="docutils literal notranslate"><span class="pre">simpleble.rst</span></code> and <code class="docutils literal notranslate"><span class="pre">modules.rst</span></code> in our <cite>Sphinx source root</cite> directory. The <code class="docutils literal notranslate"><span class="pre">modules.rst</span></code> file is usefull when more than one modules (<code class="docutils literal notranslate"><span class="pre">.py</span></code> files) are included in our Python source directory, but since we only have one module and to keep thing simple, we can ignore it for the purposes of this tutorial. Let’s have a look at the contents of <code class="docutils literal notranslate"><span class="pre">simpleble.rst</span></code>:</p>
+<p>The above command generates two files: <code class="docutils literal notranslate"><span class="pre">simpleble.rst</span></code> and <code class="docutils literal notranslate"><span class="pre">modules.rst</span></code> in our <cite>Sphinx source root</cite> directory. The <code class="docutils literal notranslate"><span class="pre">modules.rst</span></code> file is useful when more than one modules (<code class="docutils literal notranslate"><span class="pre">.py</span></code> files) are included in our Python source directory, but since we only have one module and to keep thing simple, we can ignore it for the purposes of this tutorial. Let’s have a look at the contents of <code class="docutils literal notranslate"><span class="pre">simpleble.rst</span></code>:</p>
 <div class="highlight-RST notranslate"><div class="highlight"><pre><span></span><span class="gh">simpleble module</span>
 <span class="gh">================</span>
 

docs/source/build-the-docs.rst

@@ -54,7 +54,7 @@ Now let's see how we can auto-generate documentation from the docstrings in our
     Creating file ./source/simpleble.rst.
     Creating file ./source/modules.rst.
 
-The above command generates two files: ``simpleble.rst`` and ``modules.rst`` in our `Sphinx source root` directory. The ``modules.rst`` file is usefull when more than one modules (``.py`` files) are included in our Python source directory, but since we only have one module and to keep thing simple, we can ignore it for the purposes of this tutorial. Let's have a look at the contents of ``simpleble.rst``:
+The above command generates two files: ``simpleble.rst`` and ``modules.rst`` in our `Sphinx source root` directory. The ``modules.rst`` file is useful when more than one modules (``.py`` files) are included in our Python source directory, but since we only have one module and to keep thing simple, we can ignore it for the purposes of this tutorial. Let's have a look at the contents of ``simpleble.rst``:
 
 .. code-block:: RST