update docs and contributing

docs/database/boltdb.md

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+# IronFunctions using BoltDB
+
+BoltDB is the default database, you just need to run the API.
+
+## Persistent
+
+To keep it persistent you add a volume flag to the command:
+
+```
+docker run --rm -it -v $PWD/bold.db:/app/bolt.db -p 8080:8080 iron/functions
+```

docs/database/postgres.md

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+# IronFunctions using Postgres
+
+Let's presuppose you don't have even a postgres DB ready.
+
+### 1. Let's start a postgres instance:
+
+```
+docker run --name iron-postgres \
+        -e POSTGRES_PASSWORD=ironfunctions -d postgres
+``` 
+
+### 2. Now let's create a new database to IronFunctions
+
+Creating database:
+
+```
+docker run -it --rm --link iron-postgres:postgres postgres \
+    psql -h postgres -U postgres -c "CREATE DATABASE funcs;"
+```
+
+Granting access to postgres user
+
+```
+docker run -it --rm --link iron-postgres:postgres postgres \
+    psql -h postgres -U postgres -c 'GRANT ALL PRIVILEGES ON DATABASE funcs TO postgres;'
+```
+
+### 3. Now let's start IronFunctions connecting to our new postgres instance
+
+```
+docker run --rm --link "iron-postgres:postgres" \
+    -e "DB=postgres://postgres:ironfunctions@postgres/funcs?sslmode=disable" \
+    -it -p 8080:8080 iron/functions
+```