doc: warn about SuppressDestruct() (#926)

Not sure how this ever made its way into the API, but people should *never* use this.

Author: addaleax

doc/reference.md

@@ -4,7 +4,7 @@ Holds a counted reference to a [`Napi::Value`](value.md) object; initially a wea
 
 The referenced `Napi::Value` is not immediately destroyed when the reference count is zero; it is merely then eligible for garbage-collection if there are no other references to the `Napi::Value`.
 
-`Napi::Reference` objects allocated in static space, such as a global static instance, must call the `SuppressDestruct` method to prevent its destructor, running at program shutdown time, from attempting to reset the reference when the environment is no longer valid.
+`Napi::Reference` objects allocated in static space, such as a global static instance, must call the `SuppressDestruct` method to prevent its destructor, running at program shutdown time, from attempting to reset the reference when the environment is no longer valid. Avoid using this if at all possible.
 
 The following classes inherit, either directly or indirectly, from `Napi::Reference`:
 
@@ -109,3 +109,5 @@ void Napi::Reference::SuppressDestruct();
 ```
 
 Call this method on a `Napi::Reference` that is declared as static data to prevent its destructor, running at program shutdown time, from attempting to reset the reference when the environment is no longer valid.
+
+ Avoid using this if at all possible. If you do need to use static data, **MAKE SURE** to warn your users that your addon is **NOT** threadsafe.

napi.h

@@ -1175,9 +1175,11 @@ namespace Napi {
     void Reset();
     void Reset(const T& value, uint32_t refcount = 0);
 
-    // Call this on a reference that is declared as static data, to prevent its destructor
-    // from running at program shutdown time, which would attempt to reset the reference when
-    // the environment is no longer valid.
+    // Call this on a reference that is declared as static data, to prevent its
+    // destructor from running at program shutdown time, which would attempt to
+    // reset the reference when the environment is no longer valid. Avoid using
+    // this if at all possible. If you do need to use static data, MAKE SURE to
+    // warn your users that your addon is NOT threadsafe.
     void SuppressDestruct();
 
   protected: