Add internal link to Database Settings in User Guide

[jlturriff]

Overview

The User Guide provides no information about setting up an Additional Authentication credentials; instead it says, "4. (Optional) Browse for the Key File if you have chosen it as an additional authentication factor while creating the database. ==>Refer to the KeePassXC User Guide for more information on setting a Key File as an additional authentication factor.<=="

Steps to Reproduce

1. Open the online User Guide;
2. Select "Creating Your First Database" in the navigation pane;
3. Scroll down to the description of pasword etc. entry (Can't build from source in ubuntu 16 x64 #4). This entry does not mention anything about the "Add Additional Protection..." button.
4. Select "Opening an Existing Database" in the navigation pane;
5. Scroll down to the description of pasword etc. entry; (Can't build from source in ubuntu 16 x64 #4), which says, "(Optional) Browse for the Key File if you have chosen it as an additional authentication factor while creating the database. Refer to the KeePassXC User Guide for more information on setting a Key File as an additional authentication factor."

Expected Behavior

The User Guide should provide "actual information on setting a Key File as an additional authentication factor".

Actual Behavior

The User Guide merely refers to itself, providing no such information.

Context

Fresh install.

KeePassXC - Version 2.6.2
Revision: e9b9582

Qt 5.9.7
Debugging mode is disabled.

Operating system: openSUSE Leap 15.1
CPU architecture: x86_64
Kernel: linux 4.12.14-lp151.28.75-default

Enabled extensions:

• Auto-Type
• Browser Integration
• SSH Agent
• KeeShare (signed and unsigned sharing)
• YubiKey
• Secret Service Integration

Cryptographic libraries:
libgcrypt 1.8.2

Operating System: Linux
Desktop Env: Trinity
Windowing System: X11

[droidmonkey]

It is fully covered here: https://keepassxc.org/docs/KeePassXC_UserGuide.html#_database_settings

See step 3 and 4.

Agree that an internal reference can be made though.