Replace README.txt with README.md

Patch have the following issues

git.drupalcode.org_project_masked_input_-_merge_requests_3.patch.txt:1911: trailing whitespace.
[form-element]
git.drupalcode.org_project_masked_input_-_merge_requests_3.patch.txt:5354: trailing whitespace.

git.drupalcode.org_project_masked_input_-_merge_requests_3.patch.txt:5427: trailing whitespace.

git.drupalcode.org_project_masked_input_-_merge_requests_3.patch.txt:5429: trailing whitespace.

git.drupalcode.org_project_masked_input_-_merge_requests_3.patch.txt:5431: trailing whitespace.
        //ndebug($config->get('masked_input_definitions'));
error: patch failed: masked_input.module:55
error: masked_input.module: patch does not apply
error: patch failed: src/MaskedInputSettingsForm.php:41
error: src/MaskedInputSettingsForm.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:27
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: masked_input.module:96
error: masked_input.module: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:127
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:132
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:133
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:158
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:140
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:53
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:59
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:132
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:75
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php:151
error: src/Plugin/Field/FieldWidget/MaskedinputFieldWidgetDefault.php: patch does not apply
error: patch failed: README.txt:1
error: README.txt: patch does not apply