Docker image: add entrypoint script

First of all, this script moves the duniter configuration file 'conf.json' into the '/etc/duniter' volume, so that one could delete the '/var/lib/duniter' volume without losing the configuration.

A symbolic link is set up into /var/lib/duniter/duniter_default to point to the new path: /var/lib/duniter/duniter_default/conf.json -> /etc/duniter/conf.json

Then, this script enables the folowing environment variables:

• DUNITER_MANUAL_CONFIG (boolean, default = false)

  When set to 'true' (or 'yes', or '1'), the script waits until the file '/etc/duniter/conf.json.orig' is present before starting the duniter service. Here is the workflow when enabled:

  1. wait for '/etc/duniter/conf.json.orig'
  2. if this file was changed since the previous startup: 2.1. Save 'conf.json' to 'conf.json.old' 2.2. Replace 'conf.json' with 'conf.json.orig' 2.3. Save the new file's checksum to compare with at next startup
  3. continue the startup sequence

  When set to false, the startup sequence continues.

• DUNITER_AUTO_SYNC (boolean, default = false) Requires 'DUNITER_SYNC_HOST'.

  When set to 'true' (or 'yes', or '1') and the folder '/var/lib/duniter/duniter_default/data' doesn't exist, a 'duniter sync' command will be issued before starting the service.

  When set to false, the service is started directly.

• DUNITER_SYNC_HOST (hostname, default = "")

  This is the 'host:port' parameter to use with 'duniter sync' when 'DUNITER_AUTO_SYNC' is enabled.

  The synchronization won't be launched when the wariable is not defined or empty.

doc/use/docker.md

@@ -4,7 +4,7 @@
 
 Build this image:
 
-    docker build . -t duniter/duniter
+    docker build . -t duniter/duniter -f release/docker/Dockerfile
 
 ## Usage
 
@@ -59,6 +59,41 @@ When no parameters are given, `duniter` is called with the command `direct_webst
 
 Note that you should not call duniter with daemon command (`webstart` or `start`) if you run docker with `-d` parameter, because the docker image will then immediately stop.
 
+## Environment variables
+
+To ease the deployment automation, three environment variables are available:
+
+* DUNITER_MANUAL_CONFIG (boolean, default = false)
+
+  When set to 'true' (or 'yes', or '1'), the entrypoint script waits until the file
+  '/etc/duniter/conf.json.orig' is present before starting the duniter
+  service. Here is the workflow when enabled:
+  1. wait for '/etc/duniter/conf.json.orig'
+  2. if this file was changed since the previous startup:
+     1. Save 'conf.json' to 'conf.json.old'
+     2. Replace 'conf.json' with 'conf.json.orig'
+     3. Save the new file's checksum to compare with at next startup
+  3. continue the startup sequence
+
+  When set to false, the startup sequence continues.
+
+* DUNITER_AUTO_SYNC (boolean, default = false)
+  Requires 'DUNITER_SYNC_HOST'.
+
+  When set to 'true' (or 'yes', or '1') and the folder
+  '/var/lib/duniter/duniter_default/data' doesn't exist, a 'duniter sync'
+  command will be issued before starting the service.
+
+  When set to false, the service is started directly.
+
+* DUNITER_SYNC_HOST (hostname, default = "")
+
+  This is the 'host:port' parameter to use with 'duniter sync' when
+  'DUNITER_AUTO_SYNC' is enabled.
+
+  The synchronization won't be launched when the variable is not defined
+  or empty.
+
 ## Test develop version
 
 To test develop version on G1-test network: