added documentation for wallet storage databases

Databases.md

@@ -0,0 +1,53 @@
+# Databases
+
+Your wallet stores secret keys, connections and other information.
+You have different choices to store this information.
+The wallet supports 2 different databases to store data, SQLite and PostgreSQL.
+
+## SQLite
+
+If the wallet is configured the default way in eg. [demo-args.yaml](demo/demo-args.yaml), without explicit wallet-storage, a sqlite database file is used.
+
+```yaml
+# demo-args.yaml
+wallet-type: indy
+wallet-name: wallet
+wallet-key: wallet-password
+```
+
+For this configuration, a folder called wallet will be created which contains a file called `sqlite.db`.
+
+## PostgreSQL
+
+The wallet can be configured to use PostgreSQL as storage.
+
+```yaml
+# demo-args.yaml
+wallet-type: indy
+wallet-name: wallet
+wallet-key: wallet-password
+
+wallet-storage-type: postgres_storage
+wallet-storage-config: "{\"url\":\"db:5432\",\"wallet_scheme\":\"DatabasePerWallet\"}"
+wallet-storage-creds: "{\"account\":\"postgres\",\"password\":\"mysecretpassword\",\"admin_account\":\"postgres\",\"admin_password\":\"mysecretpassword\"}"
+```
+
+In this case the hostname for the database is `db` on port 5432.
+
+A docker-compose file could look like this:
+
+```yaml
+# docker-compose.yml
+version: '3'
+services:
+  # acapy ...
+  # database
+  db:
+    image: postgres:10
+    environment:
+      POSTGRES_PASSWORD: mysecretpassword
+      POSTGRES_USER: postgres
+      POSTGRES_DB: postgres
+    ports:
+      - "5432:5432"
+```

DevReadMe.md

@@ -109,6 +109,8 @@ aca-py provision --wallet-type indy --seed $SEED
 
 For additional `provision` options, execute `aca-py provision --help`.
 
+Additional information about wallet storages can be found [here](Databases.md).
+
 ### Mediation
 
 ACA-Py can also run in mediator mode - ACA-Py can be run *as* a mediator (it can mediate connections for other agents), or it can connect to an external mediator to mediate its own connections.  See the [docs on mediation](Mediation.md) for more info.