Replace README.txt with README.md

Committed in accordance to the stated requirement

Hi @Manoj Raj.R I think you just need to rename the README.txt file to README.md.

But if you want a pattern of READMEs files in Drupal, please see the link below:

https://www.drupal.org/docs/develop/managing-a-drupalorg-theme-module-or...

I'll review it!

Everything is okay!!

The file needs more work beyond renaming the file - the headings and links should be changed to Markdown syntax, etc.

Ok! Thanks, @DamienMcKenna! I'll work on it!

Hi, @Manoj Raj.R! Your commit still need some work. I'll fix those that are left. Also, please, double check before working in a issue if someone already assigned to it to avoid re-working.

Here comes some changes. Please, kindly review it. :)

the changes look good for me. Let's see if it's approved by the mantainers, or if needs more work to keep working on it. :)

changes looks good for me

The Drupal coding standards, under Naming Conventions / File names, says:

All documentation files should have the file name extension ".txt" to make viewing them on Windows systems easier. Also, the file names for such files should be all-caps (e.g. README.txt instead of readme.txt) while the extension itself is all-lowercase (i.e. txt instead of TXT).

@apderno: That seems to be out of date and misses the point of the newer Markdown syntax files that Gitlab supports; I updated the docs page to reference the newer standard.

@DamienMcKenna It could be outdated, but until #3012906: Add Markdown to list of module documentation file types isn't closed, that is what the coding standards say.

Core already set the standard by converting to a Markdown file (#3192842: Make our README more welcoming by converting it into an "entrypoint" into the Drupal ecosystem). But we're going off-tangent here.