fix typo

ReadmeDeveloper.md

@@ -1,4 +1,4 @@
-<h1>SDRangel Developper's notes</h1>
+<h1>SDRangel Developer's notes</h1>
 
 <h2>Build options</h2>
 
@@ -215,4 +215,4 @@ The openDevice and closeDevice methods of the device interface are designed spec
   - closeDevice:
     - if there are no buddies then effectively close the device else just zero out the own copy of the device handle
     
-Exchange of dynamic information when necessary such as sample rate or center frequency is done by message passing between buddies.
+Exchange of dynamic information when necessary such as sample rate or center frequency is done by message passing between buddies.