Help: Add code example for INSTALL_INTERFACE to cmake-buildsystem.

Help/manual/cmake-buildsystem.7.rst

@@ -580,7 +580,17 @@ and the install-tree.  The ``BUILD_INTERFACE`` and ``INSTALL_INTERFACE``
 generator expressions can be used to describe separate usage requirements
 based on the usage location.  Relative paths are allowed within these
 expressions, and are interpreted relative to the current source directory
-or the installation prefix, as appropriate.
+or the installation prefix, as appropriate:
+
+.. code-block:: cmake
+
+  add_library(ClimbingStats climbingstats.cpp)
+  target_include_directories(ClimbingStats INTERFACE
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/generated>
+    $<INSTALL_INTERFACE:/absolute/path>
+    $<INSTALL_INTERFACE:relative/path>
+    $<INSTALL_INTERFACE:$<INSTALL_PREFIX>/$<CONFIG>/generated>
+  )
 
 Two convenience APIs are provided relating to include directories usage
 requirements.  The :variable:`CMAKE_INCLUDE_CURRENT_DIR_IN_INTERFACE` variable