CarpetX: Added a section in the docs detailing host, device and inlining annotations of loop lambdas

CarpetX/doc/documentation.tex

@@ -544,6 +544,32 @@ \subsection{Loop Lambdas}
   }
 \end{lstlisting}
 
+In addition, users can specify inlining (a compile-time optimization where the function call is replaced by its body) by using the \texttt{CCTK\_ATTRIBUTE\_ALWAYS\_INLINE} macro and designate host or device availability via the \texttt{CCTK\_HOST} or \texttt{CCTK\_DEVICE} macros, respectively. These annotations are optional unless the compiler is unable to build a function due to an inability to automatically determine that it needs to be available for device usage, for example. However, when these annotations are desired, they must be placed in specific locations.
+
+To mark a lambda for host usage, one would use:
+%
+\begin{lstlisting}
+  [=] CCTK_HOST(const Loop::PointDesc &p) CCTK_ATTRIBUTE_ALWAYS_INLINE {
+    // loop body
+  }
+\end{lstlisting}
+%
+For device usage, one would use:
+%
+\begin{lstlisting}
+  [=] CCTK_DEVICE(const Loop::PointDesc &p) CCTK_ATTRIBUTE_ALWAYS_INLINE {
+    // loop body
+  }
+\end{lstlisting}
+%
+For both host and device usage, one would use:
+%
+\begin{lstlisting}
+  [=] CCTK_HOST CCTK_DEVICE(const Loop::PointDesc &p) CCTK_ATTRIBUTE_ALWAYS_INLINE {
+    // loop body
+  }
+\end{lstlisting}
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \subsection{The \texttt{PointDesc} type and loop lambda body}
 \label{sec:point_des}