Doc - ArangoDB Starter Recovery Procedure (#179)

Author: sleto-it

docs/Manual/Administration/Starter/README.md

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+ArangoDB Starter Recovery Procedure
+===================================
+
+This procedure is intended to recover a cluster (that was started with the ArangoDB
+_Starter_) when a machine of that cluster is broken without the possibility to recover
+it (e.g. complete HD failure). In the procedure is does not matter if a replacement
+machine uses the old or a new IP address.
+
+To recover from this scenario, you must:
+- Create a new (replacement) machine with ArangoDB (including _Starter_) installed.
+- Create a file called `RECOVERY` in the directory you are going to use as data
+  directory of the _Starter_ (the one that is passed via the option `--starter.data-dir`).
+  This file must contain the IP address and port of the _Starter_ that has been
+  broken (and will be replaced with this new machine).
+
+E.g.
+
+```bash
+echo "192.168.1.25:8528" > $DATADIR/RECOVERY
+```
+
+After creating the `RECOVERY` file, start the _Starter_ using all the normal command
+line arguments.
+
+The _Starter_ will now:
+1) Talk to the remaining _Starters_ to find the ID of the _Starter_ it replaces and
+   use that ID to join the remaining _Starters_.
+1) Talk to the remaining _Agents_ to find the ID of the _Agent_ it replaces and
+   adjust the command-line arguments of the _Agent_ (it will start) to use that ID.
+   This is skipped if the _Starter_ was not running an _Agent_.
+1) Remove the `RECOVERY` file from the data directory.
+
+The cluster will now recover automatically. It will however have one more _Coordinators_ 
+and _DBServers_ than expected. Exactly one _Coordinator_ and one _DBServer_ will
+be listed "red" in the web UI of the database. They will have to be removed manually
+using the ArangoDB Web UI.