main: docu 2 env vars in fullhelp

NDILIB_REDIST_FOLDER and NV_OPTIMUS_ENABLEMENT (added recently; Win only)

the others env vars used by UG are not much important for regular users

Author: MartinPulec

src/main.cpp

@@ -294,6 +294,14 @@ usage(bool full = false)
                 print_help_item("--video-codecs", {"list of video codecs"});
         }
         print_help_item("address", {"destination address"});
+        if (full) {
+                color_printf("Environment variables: "
+                             TBOLD("NDILIB_REDIST_FOLDER")
+#ifdef _WIN32
+                              ", " TBOLD("NV_OPTIMUS_ENABLEMENT")
+#endif
+                             " and others (less important)\n");
+        }
         printf("\n");
 }