Add note about local header #include to install.rst

Signed-off-by: Cary Phillips <cary@ilm.com>

Author: cary-ilm

website/install.rst

@@ -145,7 +145,18 @@ include directories above; a single ``-I$prefix/include`` without the
 
 This layout preserves long-standing flat includes in existing code and
 documentation while keeping headers grouped under ``OpenEXR/`` on
-disk. There is no plan to remove either style in current release lines.
+disk. There is no plan to remove either style in current release
+lines.
+
+Also note that within the OpenEXR source tree, all local headers are
+included with quotes, i.e. ``#include "ImfHeader.h"``, not angle
+brackets ``<>``, since for an internal build the headers come from the
+same library tree. Also note that since headers are stored alongside
+source files in each internal library directory (``OpenEXR``,
+``OpenEXRCore``, ``OpenEXRUtil``, ``Iex``, ``IlmThread``), not in a
+single common ``OpenEXR`` folder, they are included internally as bare
+files, without a ``OpenEXR/`` subdirectory. This intentionally differs
+from the installed layout.
 
 OpenEXR/Imath Version Compatibility
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~