GUI, manual: some clarifications how custom user .cfg files are used (Ticket: #5847)

gui/projectfile.ui

@@ -69,6 +69,16 @@
          </item>
         </layout>
        </item>
+       <item>
+        <widget class="QLabel" name="label_8">
+         <property name="text">
+          <string>Note: Put your own custom .cfg files in the same folder as the project file. You should see them above.</string>
+         </property>
+         <property name="wordWrap">
+          <bool>true</bool>
+         </property>
+        </widget>
+       </item>
        <item>
         <layout class="QHBoxLayout" name="horizontalLayout_3">
          <item>

man/manual.docbook

@@ -713,6 +713,22 @@ Checking test.c...
     <para>If you create a configuration file for a popular library, we would
     appreciate if you upload it to us.</para>
 
+    <section>
+      <title>Using your own custom .cfg file</title>
+
+      <para>You can create and use your own .cfg files for your
+      projects.</para>
+
+      <para>The command line cppcheck will try to load custom .cfg files from
+      the working path - execute cppcheck from the path where the .cfg files
+      are.</para>
+
+      <para>The cppcheck GUI will try to load custom .cfg files from the
+      project file path. The custom .cfg files should be shown in the
+      <literal>Edit Project File</literal> dialog that you open from the
+      <literal>File</literal> menu.</para>
+    </section>
+
     <section>
       <title>Memory/resource leaks</title>