Update README.txt to README.md

Thanks, please follow the pattern under "README format" in the README.md template.

Please create an issue fork (click "Create issue fork") and commit to that, for easier preview.

I reviewed and fixed the missing newline at the end of the file and a couple of misspelling.
hope is okay now =)

Thanks to both of you! I still see issues, such as:

• Missing module name
• A capitalized header
• Code not marked up as code

Please refer to these lists for required sections and formatting:

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

Thank you for the review!
I am not sure about marking as a code, so I used markdown reference.

Thanks @lucienchalom, that was what I meant, so that was perfect. Still a few details in the list ...

Fixed the list! =)
I havent found any leading spaces tho.... sorry

They're in the list :)

 - Introduction
 - Requirements
 - Installation
 - Configuration
 - Maintainers

Should be:

- Introduction
- Requirements
- Installation
- Configuration
- Maintainers

=O
I looked at the end of the line only, sorry.
also, i found in the https://www.drupal.org/docs/develop/managing-a-drupalorg-theme-module-or...
that the numbered list uses like this

## Configuration

1. Enable the module at Administration > Extend.
1. When creating a new field on a content type or custom entity type, choose
   "Double Field" from the drop-down menu.
1. On the Field Settings form for the Double Field, define the two subfields
   as you would with any other field.

Should i change that too?

No problem, it was easily over-looked, since it was only a single space character :)

Yes please, about using just 1.'s in the ordered list. It makes them easier create and update.

Awesome!
fixed the numbered list then. =)

Looks great, thanks @anoopsingh92 and @lucienchalom!

Thank you for working on this, merged, release will follow shortly.