minor changes

README.md

@@ -305,12 +305,14 @@ ccs811_set_mode (sensor, ccs811_mode_1s);
 ...
 ```
 
-Last, the user task that uses the sensor has to be created.
+Finally, a user task that uses the sensor has to be created.
 
 ```
 xTaskCreate(user_task, "user_task", 256, NULL, 2, 0);
 ```
 
+**Please note:** To avoid concurrency situations when driver functions are used to access the sensor, for example to read data, the user task must not be created until the sensor configuration is completed.
+
 The user task can use different approaches to fetch new data. Either new data are fetched periodically or the interrupt signal *nINT* is used when new data are available or eCO2 value exceeds defined thresholds.
 
 If new data are fetched **periodically** the implementation of the user task is quite simply and could look like following.
@@ -564,6 +566,8 @@ void user_init(void)
         // start periodic measurement with one measurement per second
         ccs811_set_mode (sensor, ccs811_mode_1s);
     }
+    else
+        printf("Could not initialize CCS811 sensor\n");
 }
 
 ```

main/ccs811_example.c

@@ -174,5 +174,7 @@ void user_init(void)
         // start periodic measurement with one measurement per second
         ccs811_set_mode (sensor, ccs811_mode_1s);
     }
+    else
+        printf("Could not initialize CCS811 sensor\n");
 }