add postgres and mysql docs

docs/importer/adaptors/mysql.md

+# MYSQL
+
+MYSQL adaptor works for a MySQL Server.
+
+A basic config.env looks like the following.
+Notice how the database information is being passed as the source.
+
+```ini
+src.type=mysql
+src.uri=USER:PASSWORD@tcp(HOST:PORT)/DBNAME
+
+dest.type=elasticsearch
+dest.uri=https://USER:PASSWORD@SERVER/INDEX
+```
+
+For other types of source URIs that are supported, visit [go-sql-driver/mysql](https://github.com/go-sql-driver/mysql#examples)'s GitHub page. 

docs/importer/adaptors/postgres.md

+# PostgreSQL
+
+The [PostgreSQL](https://www.postgresql.org/) adaptor is capable of reading and tailing databases.
+
+
+### Example
+
+```ini
+src.type=postgres
+src.uri=postgres://127.0.0.1:5432/test
+tail=true
+
+dest.type=elasticsearch
+dest.uri=https://USER:PASSWORD@SERVER/INDEX
+```
+
+
+### Notes
+
+1. When using postgres as source, append `?sslmode=disable` to the uri to disable ssl otherwise you will have to put a certificate. 
+
+#### Tailing
+
+1. When using `tail: true` with postgres, you might get the error `must be superuser or replication role to use replication slots`. You need a [REPLICATION role](https://www.postgresql.org/docs/9.1/static/sql-createrole.html) for this to work. (See [ALTER role](https://www.postgresql.org/docs/9.0/static/sql-alterrole.html))
+2. When tailing, you might have to [create replication slots](https://medium.com/@tk512/replication-slots-in-postgresql-b4b03d277c75). Also set `wal_level`. 
+```ini
+wal_level=logical
+max_replication_slots=1
+``` 
+3. Create a logical replication slot for the source database. ([Logical](https://www.postgresql.org/docs/9.5/static/logicaldecoding-example.html))
+```sql
+select * from pg_create_logical_replication_slot('standby_replication_slot', 'test_decoding');
+SELECT * FROM pg_replication_slots ;
+```
+4. Make sure you see the `database name` in replication slot row. Now update `replication_slot` parameter of pipeline.js to 'standby_replication_slot'
+
+* [Delete Replication slots](https://stackoverflow.com/questions/30854961/)