Add section starting page and improve TBank SDK documentation

Introduced a new Section-Starting-Page for better navigation. Enhanced `tbank-payments-fps.md` with return values description and restructured TBank-SDK title for clarity. Updated table of contents in `rw.tree` to reflect these changes.

Author: GamerVII-NET

Writerside/topics/server-install-from-source.md

@@ -79,6 +79,9 @@ PORT_GML_FRONTEND=5003
 PORT_GML_FILES=5005
   # Сервис скинов
 PORT_GML_SKINS=5006
+
+  # Микросервисы:
+SERVICE_TEXTURE_ENDPOINT=http://gml-web-skins:8085
 ```
 
 Отредактируйте или создайте файл `.env` в папке `src\Gml.Web.Client\.env`