Expand comment for new interkeeper() function

matplotlibcpp.h

@@ -103,8 +103,14 @@ struct _interpreter {
 
     /* For now, _interpreter is implemented as a singleton since its currently not possible to have
        multiple independent embedded python interpreters without patching the python source code
-       or starting a separate process for each.
-        http://bytes.com/topic/python/answers/793370-multiple-independent-python-interpreters-c-c-program
+       or starting a separate process for each. [1]
+       Furthermore, many python objects expect that they are destructed in the same thread as they
+       were constructed. [2] So for advanced usage, a `kill()` function is provided so that library
+       users can manually ensure that the interpreter is constructed and destroyed within the
+       same thread.
+
+         1: http://bytes.com/topic/python/answers/793370-multiple-independent-python-interpreters-c-c-program
+         2: https://github.com/lava/matplotlib-cpp/pull/202#issue-436220256
        */
 
     static _interpreter& get() {
@@ -115,6 +121,7 @@ struct _interpreter {
         return interkeeper(true);
     }
 
+    // Stores the actual singleton object referenced by `get()` and `kill()`.
     static _interpreter& interkeeper(bool should_kill) {
         static _interpreter ctx;
         if (should_kill)