doc: a note about ENTT_INSTALL - close #1265

README.md

@@ -232,7 +232,8 @@ build system of the library.
 ## CMake
 
 To use `EnTT` from a `CMake` project, just link an existing target to the
-`EnTT::EnTT` alias.<br/>
+`EnTT::EnTT` alias.
+
 The library offers everything you need for locating (as in `find_package`),
 embedding (as in `add_subdirectory`), fetching (as in `FetchContent`) or using
 it in many of the ways that you can think of and that involve `CMake`.<br/>
@@ -240,6 +241,11 @@ Covering all possible cases would require a treatise and not a simple README
 file, but I'm confident that anyone reading this section also knows what it's
 about and can use `EnTT` from a `CMake` project without problems.
 
+Note that all `install` calls are guarded by the `ENTT_INSTALL` option to allow
+using `EnTT` as a submodule without conflicting with user logic.<br/>
+It is therefore necessary to set the option to true to take advantage of the
+installation logic provided by this library.
+
 ## Natvis support
 
 When using `CMake`, just enable the option `ENTT_INCLUDE_NATVIS` and enjoy