Describe 'theme' field of config-info in REST API documentation

Change-Id: Ic59e0da7375c35dd33b281f783eaf70bbd080ac3
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/Documentation/rest-api-projects.txt b/Documentation/rest-api-projects.txt
index d6da805..0f01b58 100644
--- a/Documentation/rest-api-projects.txt
+++ b/Documentation/rest-api-projects.txt
@@ -1095,6 +1095,9 @@
 configuration, which has the same format as the
 link:config-gerrit.html#_a_id_commentlink_a_section_commentlink[
 commentlink section] of `gerrit.config`.
+|`theme`                      |optional|
+The theme that is configured for the project as a link:#theme-info[
+ThemeInfo] entity.
 |==========================================
 
 [[dashboard-info]]
@@ -1320,6 +1323,22 @@
 |`size_of_packed_objects`  |Size of packed objects in bytes.
 |======================================
 
+[[theme-info]]
+ThemeInfo
+~~~~~~~~~
+The `ThemeInfo` entity describes a theme.
+
+[options="header",width="50%",cols="1,^2,4"]
+|=============================
+|Field Name      ||Description
+|`css`           |optional|
+The path to the `GerritSite.css` file.
+|`header`        |optional|
+The path to the `GerritSiteHeader.html` file.
+|`footer`        |optional|
+The path to the `GerritSiteFooter.html` file.
+|=============================
+
 
 GERRIT
 ------