Updated installation.md with respect to information about CVAT_HOST for local installation

[anugrahasinha]

Resolves #4013

Motivation and context

The installation guide should mention about exporting CVAT_HOST variable so that CVAT can be access over the network. The current installation method only supports accessing CVAT using http://localhost:8080. This information about exporting CVAT_HOST variable can be derived from AWS-Deployment Guide
source here
actual here

How has this been tested?

This is document level change, therefore the markdown has been checked for sanity.

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[nmanovic]

@anugrahasinha , thanks for your contribution! Great job. I will merge the PR after all linter checks are passed.

[anugrahasinha]

Thanks for merging the PR. 👍