formats.javaProperties: Add documentation

nixos/doc/manual/development/settings-options.section.md

@@ -32,6 +32,20 @@ type of this option should represent the format. The most common formats
 have a predefined type and string generator already declared under
 `pkgs.formats`:
 
+`pkgs.formats.javaProperties` { *`comment`* ? `"Generated with Nix"` }
+
+:   A function taking an attribute set with values
+
+    `comment`
+
+    :   A string to put at the start of the
+        file in a comment. It can have multiple
+        lines.
+
+    It returns the `type`: `attrsOf str` and a function
+    `generate` to build a Java `.properties` file, taking
+    care of the correct escaping, etc.
+
 `pkgs.formats.json` { }
 
 :   A function taking an empty attribute set (for future extensibility)

nixos/doc/manual/from_md/development/settings-options.section.xml

@@ -53,6 +53,38 @@
       <literal>pkgs.formats</literal>:
     </para>
     <variablelist>
+      <varlistentry>
+        <term>
+          <literal>pkgs.formats.javaProperties</literal> {
+          <emphasis><literal>comment</literal></emphasis> ?
+          <literal>&quot;Generated with Nix&quot;</literal> }
+        </term>
+        <listitem>
+          <para>
+            A function taking an attribute set with values
+          </para>
+          <variablelist>
+            <varlistentry>
+              <term>
+                <literal>comment</literal>
+              </term>
+              <listitem>
+                <para>
+                  A string to put at the start of the file in a comment.
+                  It can have multiple lines.
+                </para>
+              </listitem>
+            </varlistentry>
+          </variablelist>
+          <para>
+            It returns the <literal>type</literal>:
+            <literal>attrsOf str</literal> and a function
+            <literal>generate</literal> to build a Java
+            <literal>.properties</literal> file, taking care of the
+            correct escaping, etc.
+          </para>
+        </listitem>
+      </varlistentry>
       <varlistentry>
         <term>
           <literal>pkgs.formats.json</literal> { }