docs: added ru readme file for landing (#85)

README-ru.md

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+# @gravity-ui/date-utils
+
+Утилиты для управления датой и временем.
+
+## Установка
+
+```shell
+npm i @gravity-ui/date-utils
+```
+
+## Использование
+
+```typescript
+import {dateTimeParse, dateTime} from '@gravity-ui/date-utils';
+
+// Current date: 2021-08-07T12:10:00
+// User's time zone: Europe/Istanbul
+
+const FORMAT = 'YYYY-MM-DDTHH:mm:ssZ';
+
+// parse absolute date
+dateTimeParse({year: 2021, month: 7, day: 7})?.format(FORMAT); // "2021-08-07T00:00:00+03:00"
+dateTimeParse([2021, 7, 7])?.format(FORMAT); // "2021-08-07T00:00:00+03:00"
+dateTimeParse('2021-08-07')?.format(FORMAT); // "2021-08-07T00:00:00+03:00"
+dateTimeParse(1621708204063)?.format(FORMAT); // "2021-05-22T21:30:04+03:00"
+dateTimeParse('')?.format(FORMAT); // undefined
+dateTimeParse('incorrect-date')?.format(FORMAT); // undefined
+
+// parse relative date
+dateTimeParse('now')?.format(FORMAT); // "2021-08-07T12:10:00+03:00"
+dateTimeParse('now-1d')?.format(FORMAT); // "2021-08-06T12:10:00+03:00"
+dateTimeParse('now-1d+1M')?.format(FORMAT); // "2021-09-06T12:10:00+03:00"
+dateTimeParse('now/d')?.format(FORMAT); // "2021-08-07T00:00:00+03:00"
+dateTimeParse('now+1d/d')?.format(FORMAT); // "2021-08-08T00:00:00+03:00"
+dateTimeParse('now-1f')?.format(FORMAT); // undefined
+
+// create dateTime
+dateTime().format(FORMAT); // "2021-08-07T12:10:00+03:00"
+dateTime({input: '2021-08-07'}).format(FORMAT); // "2021-08-07T00:00:00+03:00"
+dateTime({input: '2021-08-07', format: 'YYYY-MM-DD'}).format(FORMAT); // "2021-08-07T00:00:00+03:00"
+dateTime({timeZone: 'Asia/Tokyo'}).format(FORMAT); // "2021-08-07T18:10:00+09:00
+dateTime({input: ''}).format(FORMAT); // "Invalid Date"
+dateTime({input: '2021-08', format: 'YYYY-MM-DD'}).format(FORMAT); // "Invalid Date"
+```
+
+## Настройки
+
+```typescript
+import {settings} from '@gravity-ui/date-utils';
+
+// Locales management
+settings.getLocale(); // default locale "en"
+settings.loadLocale('de').then(() => {
+  settings.setLocale('de');
+  settings.getLocale(); // "de"
+});
+
+// Customization
+settings.updateLocale({weekStart: 0}); // change first day of week
+```