Merge pull request dragonflyoss#555 from lowzj/faq-logOfTask

docs: get all dfget logs of a task in dfclient.log

FAQ.md

@@ -259,3 +259,23 @@ User can get dfget's log from file `$HOME/.small-dragonfly/logs/dfclient.log`, a
 # download from other dfget peer
 2019-02-13 15:22:40.062 INFO sign:32047-1550042560.044 : downloading piece:{"taskID":"b4b0f175f7aef583ff6ff8da6b00024d7772b165caa66ff8ef3a9dce6701b690","superNode":"127.0.0.1","dstCid":"127.0.0.1-31923-1550042443.708","range":"0-4194303","result":503,"status":701,"pieceSize":4194304,"pieceNum":0}
 ```
+
+## How to view all the dfget logs of a task
+
+You can follow the steps:
+
+- find a failed task: `grep 'download FAIL' dfclient.log`, such as:
+
+  ```
+  2019-05-22 05:40:58.120 INFO sign:38923-1558496382.915 : download FAIL cost:75.208s length:4120442 reason:0
+  ```
+
+- get all the logs of this task through the sign `38923-1558496382.915`: `grep 38923-1558496382.915 dfclient.log`, such as:
+
+  ```
+  2019-05-22 05:39:42.919 INFO sign:38923-1558496382.915 : get cmd params:["dfget" "-u" "https://xxx" "-o" "./a.test"]
+  ...
+  ...
+  2019-05-22 05:40:58.120 INFO sign:38923-1558496382.915 : download FAIL cost:75.208s length:4120442 reason:0
+  ```
+

README.md

@@ -87,9 +87,9 @@ Other active channels:
 - Twitter: [@dragonfly_oss](https://twitter.com/dragonfly_oss)
 - Dingtalk Group(钉钉群)
 
-<p align="center">
-<img src=https://user-images.githubusercontent.com/9465626/50591975-2ac2ba00-0ecd-11e9-9e53-4c4d6a7dfc7d.jpg width="250">
-</p>
+<div align="center">
+  <img src="docs/images/df-dev-dingtalk.png" width="250" title="dingtalk">
+</div>
 
 ## Contributing