Add v3.1 release (#123)

* Update README

* Set docker mirror version to v3.1.0

Author: Aiee

docker-compose.yaml

@@ -1,7 +1,7 @@
 version: '3.4'
 services:
   metad0:
-    image: vesoft/nebula-metad:nightly
+    image: vesoft/nebula-metad:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -35,7 +35,7 @@ services:
       - SYS_PTRACE
 
   metad1:
-    image: vesoft/nebula-metad:nightly
+    image: vesoft/nebula-metad:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -69,7 +69,7 @@ services:
       - SYS_PTRACE
 
   metad2:
-    image: vesoft/nebula-metad:nightly
+    image: vesoft/nebula-metad:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -103,7 +103,7 @@ services:
       - SYS_PTRACE
 
   storaged0:
-    image: vesoft/nebula-storaged:nightly
+    image: vesoft/nebula-storaged:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -141,7 +141,7 @@ services:
       - SYS_PTRACE
 
   storaged1:
-    image: vesoft/nebula-storaged:nightly
+    image: vesoft/nebula-storaged:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -179,7 +179,7 @@ services:
       - SYS_PTRACE
 
   storaged2:
-    image: vesoft/nebula-storaged:nightly
+    image: vesoft/nebula-storaged:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -217,7 +217,7 @@ services:
       - SYS_PTRACE
 
   graphd:
-    image: vesoft/nebula-graphd:nightly
+    image: vesoft/nebula-graphd:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -253,7 +253,7 @@ services:
       - SYS_PTRACE
 
   graphd1:
-    image: vesoft/nebula-graphd:nightly
+    image: vesoft/nebula-graphd:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -289,7 +289,7 @@ services:
       - SYS_PTRACE
 
   graphd2:
-    image: vesoft/nebula-graphd:nightly
+    image: vesoft/nebula-graphd:v3.1.0
     environment:
       USER: root
       TZ:   "${TZ}"
@@ -325,7 +325,7 @@ services:
       - SYS_PTRACE
 
   console:
-    image: vesoft/nebula-console:nightly
+    image: vesoft/nebula-console:v3.0.0
     entrypoint: ""
     command: 
       - sh