[libsigcplusplus] Reference docs: main page: Discourage multiple PKG_CHECK_MODULES() calls.

[Murray Cumming <murrayc src gnome org>]

commit c15977f587d06254ce6f08ac27cc6d3e5087b274
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Mar 15 12:34:51 2016 +0100

    Reference docs: main page: Discourage multiple PKG_CHECK_MODULES() calls.
    
    Mention that one PKG_CHECK_MODULES() call can check for all
    pgk-config-based dependencies.

 sigc++/sigc++.h |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/sigc++/sigc++.h b/sigc++/sigc++.h
index 064c6b3..68442b5 100644
--- a/sigc++/sigc++.h
+++ b/sigc++/sigc++.h
@@ -78,6 +78,9 @@
  * yourprogram_LDADD = $(DEPS_LIBS)
  * @endcode
  *
+ * Your PKG_CHECK_MODULES() call should also mention any other libraries that
+ * you need to use via pkg-config.
+ *
  * @subsection cmake Using CMake
  *
  * If using CMake, use the following in @c CMakeList.txt:
@@ -88,6 +91,9 @@
  * target_link_libraries(yourprogram ${DEPS_LIBRARIES})
  * @endcode
  *
+ * Your pkg_check_modules() call should also mention any other libraries that
+ * you need to use via pkg-config.
+ *
  * @section scope Scope of Documentation
  *
  * libsigc++ contains many template functions and template classes/structs,