Emphasize in guides that all this is optional.

0400-Compilation-Linux.md

@@ -12,6 +12,8 @@ In order to exploit INMOST library in parallel you have to provide any Message P
 
 [[Compile INMOST|0402-Compilation-INMOST-Linux]]
 
+The following guides will show how to compile INMOST with optional third party packages.
+
 [[Compile INMOST with PETSc|0403-Compilation-PETSc-Linux]]
 
 [[Compile INMOST with Trilinos|0404-Compilation-Trilinos-Linux]]