update documentation on rtl-sdr SN

src/components/pages/device/config.vue

@@ -60,7 +60,7 @@
                       <label for="rtlDeviceId">Device index</label>
                       <input type="number" id="rtlDeviceId" name="rtlDeviceId" :class="{'is-invalid': errors.has('rtlDeviceId') }" v-validate="'required|integer'" class="form-control" v-model.number="entity.rtlDeviceId">
                       <div class="invalid-feedback" v-if="errors.has('rtlDeviceId')">{{ errors.first('rtlDeviceId') }}</div>
-                      <small id="rtlDeviceIdHelp" class="form-text text-muted">If several rtl-sdr devices connected specify index here to distinguish them</small>
+                      <small id="rtlDeviceIdHelp" class="form-text text-muted">If several rtl-sdr devices connected specify index here or SN (serial number) to distinguish them</small>
                     </div>
                 </div>
                 <div class="col-md-4">