Add doc note about threading and use OSThread to make GPIO watching work

Thanks to @mc-hamster for the idea

src/plugins/RemoteHardwarePlugin.h

@@ -1,17 +1,26 @@
 #pragma once
 #include "ProtobufPlugin.h"
 #include "remote_hardware.pb.h"
+#include "concurrency/OSThread.h"
 
 /**
  * A plugin that provides easy low-level remote access to device hardware.
  */
-class RemoteHardwarePlugin : public ProtobufPlugin<HardwareMessage>
+class RemoteHardwarePlugin : public ProtobufPlugin<HardwareMessage>, private concurrency::OSThread
 {
+    /// The current set of GPIOs we've been asked to watch for changes
+    uint64_t watchGpios = 0; 
+
+    /// The previously read value of watched pins
+    uint64_t previousWatch = 0;
+
+    /// The timestamp of our last watch event (we throttle watches to 1 change every 30 seconds)
+    uint32_t lastWatchMsec = 0;
   public:
     /** Constructor
      * name is for debugging output
      */
-    RemoteHardwarePlugin() : ProtobufPlugin("remotehardware", PortNum_REMOTE_HARDWARE_APP, HardwareMessage_fields) {}
+    RemoteHardwarePlugin();
 
   protected:
     /** Called to handle a particular incoming message
@@ -19,6 +28,16 @@ class RemoteHardwarePlugin : public ProtobufPlugin<HardwareMessage>
     @return true if you've guaranteed you've handled this message and no other handlers should be considered for it
     */
     virtual bool handleReceivedProtobuf(const MeshPacket &mp, const HardwareMessage &p);
+
+    /**
+     * Periodically read the gpios we have been asked to WATCH, if they have changed,
+     * broadcast a message with the change information.
+     * 
+     * The method that will be called each time our thread gets a chance to run
+     *
+     * Returns desired period for next invocation (or RUN_SAME for no change)
+     */
+    virtual int32_t runOnce();
 };
 
 extern RemoteHardwarePlugin remoteHardwarePlugin;