doc: fix installation guide, add doc build info part 2

README.md

@@ -42,6 +42,15 @@ We are using `mkdocs` to build the documentation. To build and deploy the docume
 We need to set the `CHARTS_FIELDS` for our custom handler, that autogenerate documentation
 for chart types fields.
 
+The CKAN instance will be initialized, because we will call validators and helpers in this code. Therefore, you'll need
+another environment variable to set the CKAN configuration file path:
+
+    export CKAN_INI=$PWD/config/ckan.ini
+
+The config file must enable the `ckanext-charts` plugin:
+
+    ckan.plugins = ... charts_view charts_builder_view ...
+
 If you're working on the documentation, you can run the following command to start a live-reloading server without
 gathering the chart types fields data. It will speed up the process significantly, as we won't need to wait for the
 CKAN initialization:

site/index.html

@@ -1066,6 +1066,13 @@ <h2 id="building-the-documentation">Building the documentation</h2>
 </code></pre>
 <p>We need to set the <code>CHARTS_FIELDS</code> for our custom handler, that autogenerate documentation
 for chart types fields.</p>
+<p>The CKAN instance will be initialized, because we will call validators and helpers in this code. Therefore, you'll need
+another environment variable to set the CKAN configuration file path:</p>
+<pre><code>export CKAN_INI=$PWD/config/ckan.ini
+</code></pre>
+<p>The config file must enable the <code>ckanext-charts</code> plugin:</p>
+<pre><code>ckan.plugins = ... charts_view charts_builder_view ...
+</code></pre>
 <p>If you're working on the documentation, you can run the following command to start a live-reloading server without
 gathering the chart types fields data. It will speed up the process significantly, as we won't need to wait for the
 CKAN initialization:</p>