smp: add some overview docs on the related minimal example

minimal-examples/http-server/minimal-http-server-smp/README.md

@@ -1,5 +1,20 @@
 # lws minimal http server with multithreaded service
 
+Lws supports multithreaded service... build lws with `-DLWS_MAP_SMP=<max number of threads>`, the
+default is 1.  If nonzero, some extra pthreads locking is built into lws and it supports multiple
+independent service threads.
+
+![lws-smp-overview](../../../doc-assets/lws-smp-ov.png)
+
+When an incoming connection is accepted, it is bound to the pt with the lowest current wsi
+count, to keep the load on the threads balanced.  Only the pt the wsi is bound to can service
+the thread, so although there can be as many wsi being serviced simultaneously as there are
+service threads, a wsi can only be service by the pt it is bound to.
+
+The effectiveness of the scalability depends on the load.  Here is an example of roughly what can be expected
+
+![lws-smp-example](../../../doc-assets/lws-smp-example.png)
+
 ## build
 
 ```