Replace README.txt with README.md and update README.md file

Created MR for the issue, please review.

Thanks.

Tested the MR1 and got these warnings on applying the patch:

readme.patch:22: trailing whitespace.
Views PgwSlider module integrates the
readme.patch:23: trailing whitespace.
PgwSlider
readme.patch:66: trailing whitespace.
1. Download the 'Views PgwSlider' module archive. Extract and place it in the
readme.patch:69: trailing whitespace.
3. Download and extract the PgwSlider plugin and place it in libraries directory
readme.patch:78: trailing whitespace.
1. Create a new Content Type with an image field (set max of 1 image
warning: squelched 2 whitespace errors
warning: 7 lines add whitespace errors.

"Ordered lists use "1", for easier updates and to avoid errors"

The patch works fine. Moving it to RTBC

Since the last reviewer does not pay much attention to details, it would be better somebody else reviews the MR/patch.

Reviewed MR!1, The patch is not cleanly applied.

1. Change "## Contents of this file" to "## Table of contents".
2. Change Number order to 1, 2, 3
3. Configuration section is missing.

Reviewed MR!1, the patch is not cleanly applied.

git.drupalcode.org_project_views_pgwslider_-_merge_requests_1.diff.txt:114: trailing whitespace.
+Views PgwSlider module integrates the
git.drupalcode.org_project_views_pgwslider_-_merge_requests_1.diff.txt:115: trailing whitespace.
+<a href="https://github.com/Pagawa/PgwSlider" target="_blank">PgwSlider</a>
git.drupalcode.org_project_views_pgwslider_-_merge_requests_1.diff.txt:158: trailing whitespace.
+1. Download the 'Views PgwSlider' module archive. Extract and place it in the
git.drupalcode.org_project_views_pgwslider_-_merge_requests_1.diff.txt:161: trailing whitespace.
+3. Download and extract the PgwSlider plugin and place it in libraries directory
git.drupalcode.org_project_views_pgwslider_-_merge_requests_1.diff.txt:170: trailing whitespace.
+1. Create a new Content Type with an image field (set max of 1 image
warning: squelched 5 whitespace errors
warning: 10 lines add whitespace errors.


2. Change Number order to 1, 2, 3
3. Configuration section is missing.

Changes are pushed to 8.x-1.x branch. MR as a patch will not apply as the changes are already there. Please review the file as per README.md template.

As per the Drupal Readme.md template, configuration section is missing and also lists needs formatting.
Changing Back to NW