updated README (added a note on EnTT and shared libraries - see #111)

README.md

@@ -264,6 +264,46 @@ Use the line below to include only the entity-component system instead:
 Then pass the proper `-I` argument to the compiler to add the `src` directory to
 the include paths.
 
+### Side note: shared libraries
+
+To make sure that an application and a shared library that use both `EnTT` can
+interact correctly when symbols are hidden by default, there are some tricks to
+follow.<br/>
+In particular and in order to avoid undefined behaviors, all the instantiation
+of the `Family` class template shall be made explicit along with the system-wide
+specifier to use to export them.
+
+At the time I'm writing this document, the classes that use internally the above
+mentioned class template are `Dispatcher`, `Emitter` and `Registry`. Therefore
+and as an example, if you use the `Registry` class template in your shared
+library and want to set symbols visibility to _hidden_ by default, the following
+lines are required to allow it to function properly with a client that also uses
+the `Registry` somehow:
+
+* On GNU/Linux:
+
+  ```cpp
+  namespace entt {
+      template class __attribute__((visibility("default"))) Family<struct InternalRegistryTagFamily>;
+      template class __attribute__((visibility("default"))) Family<struct InternalRegistryComponentFamily>;
+      template class __attribute__((visibility("default"))) Family<struct InternalRegistryHandlerFamily>;
+  }
+  ```
+
+* On Windows:
+
+  ```cpp
+  namespace entt {
+      template class __declspec(dllexport) Family<struct InternalRegistryTagFamily>;
+      template class __declspec(dllexport) Family<struct InternalRegistryComponentFamily>;
+      template class __declspec(dllexport) Family<struct InternalRegistryHandlerFamily>;
+  }
+  ```
+
+Otherwise, the risk is that type identifiers are different between the shared
+library and the application and this will prevent the whole thing from
+functioning correctly for obvious reasons.
+
 ## Documentation
 
 The documentation is based on [doxygen](http://www.stack.nl/~dimitri/doxygen/).