Add docfx conceptual docs

(cherry picked from commit ccf3aa8)

doc/index.md

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+---
+layout: doc
+title: Entity Framework 6
+---
+
+Npgsql has an Entity Framework 6 provider. You can use it by installing the
+[EntityFramework6.Npgsql](https://www.nuget.org/packages/EntityFramework6.Npgsql/) nuget.
+
+## Guid Support ##
+
+Npgsql EF migrations support uses `uuid_generate_v4()` function to generate guids.
+In order to have access to this function, you have to install the extension uuid-ossp through the following command:
+
+```sql
+create extension "uuid-ossp";
+```
+
+If you don't have this extension installed, when you run Npgsql migrations you will get the following error message:
+
+```
+ERROR:  function uuid_generate_v4() does not exist
+```
+
+If the database is being created by Npgsql Migrations, you will need to
+[run the `create extension` command in the `template1` database](http://stackoverflow.com/a/11584751).
+This way, when the new database is created, the extension will be installed already.
+
+## Template Database ##
+
+When the Entity Framework 6 provider creates a database, it issues a simple `CREATE DATABASE` command.
+In PostgreSQL, this implicitly uses `template1` as the template - anything existing in `template1` will
+be copied to your new database. If you wish to change the database used as a template, you can specify
+the `EF Template Database` connection string parameter. For more info see the
+[PostgreSQL docs](https://www.postgresql.org/docs/current/static/sql-createdatabase.html).

doc/toc.md

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+# [Getting Started](index.md)