Update Geo documentation to use `primary` and `secondary` terminology.

doc/gitlab-geo/README.md

@@ -54,7 +54,7 @@ Geo instances. Follow the steps below in the order that they appear:
 
 1. Install GitLab Enterprise Edition on the server that will serve as the
    secondary Geo node
-1. [Setup a database replication](./database.md) in `master <-> slave` topology
+1. [Setup a database replication](./database.md) in `primary <-> secondary (read-only)` topology
 1. [Configure GitLab](configuration.md) and set the primary and secondary nodes
 After you set up the database replication and configure the GitLab Geo nodes,
 there are a few things to consider:

doc/gitlab-geo/configuration.md

@@ -81,8 +81,8 @@ Host example.com                    # The FQDN of the primary Geo node
 ## Primary Node GitLab setup
 
 >**Note:**
-You will need to setup your database into a **Master <-> Slave** replication
-topology, and your Primary node should always point to a database's Master
+You will need to setup your database into a **Primary <-> Secondary (read-only)** replication
+topology, and your Primary node should always point to a database's Primary
 instance. If you haven't done that already, read [database replication](./database.md).
 
 Go to the server that you chose to be your primary, and visit

doc/gitlab-geo/database.md

@@ -4,12 +4,13 @@ This document describes the minimal steps you have to take in order to
 replicate your GitLab database into another server. You may have to change
 some values according to your database setup, how big it is, etc.
 
-The GitLab primary node where the write operations happen will act as `master`,
-and the secondary ones which are read-only will act as `slaves`.
+The GitLab primary node where the write operations happen will connect to
+`primary` database server, and the secondary ones which are read-only will
+connect to `secondary` database servers (which are read-only too).
 
 >**Note:**
-To be on par with GitLab's notation, we will use `primary` to denote the `master`
-server, and `secondary` for the `slave`.
+In many databases documentation you will see `primary` being references as `master`
+and `secondary` as either `slave` or `standby` server (read-only).
 
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