Replace README.txt with README.md

I verified and applied MR !1 for Drupal version 10.0.2.
README.txt file updated to README.md after applying MR but got some warning
Adding screenshots for reference:

1.diff.patch:817: trailing whitespace.
    form_set_error('outvoice', t("Please enter an amount larger than $1. To publish without using outvoice,
1.diff.patch:825: trailing whitespace.
    form_set_error('outvoice', t("You are not authorized for amounts greater than $10000. To publish without using outvoice,
warning: 2 lines add whitespace errors.

Anjali Mehta → made their first commit to this issue’s fork.

Reviewed MR!1, the patch still has some issues.

1.diff.txt:816: trailing whitespace.
    form_set_error('outvoice', t("Please enter an amount larger than $1. To publish without using outvoice,
1.diff.txt:824: trailing whitespace.
    form_set_error('outvoice', t("You are not authorized for amounts greater than $10000. To publish without using outvoice,
1.diff.txt:216: new blank line at EOF.
+
warning: 3 lines add whitespace errors.

Reviewed MR!1, the file is updated as per readme.md file template.
Hence marking it to RTBC.