chore: add isDuration description to readme

Author: os-moussao

README.md

@@ -105,6 +105,7 @@ Validator                               | Description
 **isDate(str [, options])**          | check if the string is a valid date. e.g. [`2002-07-15`, new Date()].<br/><br/> `options` is an object which can contain the keys `format`, `strictMode` and/or `delimiters`.<br/><br/>`format` is a string and defaults to `YYYY/MM/DD`.<br/><br/>`strictMode` is a boolean and defaults to `false`. If `strictMode` is set to true, the validator will reject strings different from `format`.<br/><br/> `delimiters` is an array of allowed date delimiters and defaults to `['/', '-']`.
 **isDecimal(str [, options])**             | check if the string represents a decimal number, such as 0.1, .3, 1.1, 1.00003, 4.0, etc.<br/><br/>`options` is an object which defaults to `{force_decimal: false, decimal_digits: '1,', locale: 'en-US'}`.<br/><br/>`locale` determines the decimal separator and is one of `['ar', 'ar-AE', 'ar-BH', 'ar-DZ', 'ar-EG', 'ar-IQ', 'ar-JO', 'ar-KW', 'ar-LB', 'ar-LY', 'ar-MA', 'ar-QA', 'ar-QM', 'ar-SA', 'ar-SD', 'ar-SY', 'ar-TN', 'ar-YE', 'bg-BG', 'cs-CZ', 'da-DK', 'de-DE', 'el-GR', 'en-AU', 'en-GB', 'en-HK', 'en-IN', 'en-NZ', 'en-US', 'en-ZA', 'en-ZM', 'eo', 'es-ES', 'fa', 'fa-AF', 'fa-IR', 'fr-FR', 'fr-CA', 'hu-HU', 'id-ID', 'it-IT', 'ku-IQ', 'nb-NO', 'nl-NL', 'nn-NO', 'pl-PL', 'pl-Pl', 'pt-BR', 'pt-PT', 'ru-RU', 'sl-SI', 'sr-RS', 'sr-RS@latin', 'sv-SE', 'tr-TR', 'uk-UA', 'vi-VN']`.<br/>**Note:** `decimal_digits` is given as a range like '1,3', a specific value like '3' or min like '1,'.
 **isDivisibleBy(str, number)**          | check if the string is a number that is divisible by another.
+**isDuration(str)**                     | check if the string is a valid duration. e.g. [`1 week`, `2 days`, `1h`, `30m`, `15 s`].<br/><br/>It is designed to match the format used by the [ms](https://github.com/vercel/ms) package.
 **isEAN(str)**                          | check if the string is an [EAN (European Article Number)][European Article Number].
 **isEmail(str [, options])**            | check if the string is an email.<br/><br/>`options` is an object which defaults to `{ allow_display_name: false, require_display_name: false, allow_utf8_local_part: true, require_tld: true, allow_ip_domain: false, allow_underscores: false, domain_specific_validation: false, blacklisted_chars: '', host_blacklist: [] }`. If `allow_display_name` is set to true, the validator will also match `Display Name <email-address>`. If `require_display_name` is set to true, the validator will reject strings without the format `Display Name <email-address>`. If `allow_utf8_local_part` is set to false, the validator will not allow any non-English UTF8 character in email address' local part. If `require_tld` is set to false, email addresses without a TLD in their domain will also be matched. If `ignore_max_length` is set to true, the validator will not check for the standard max length of an email. If `allow_ip_domain` is set to true, the validator will allow IP addresses in the host part. If `domain_specific_validation` is true, some additional validation will be enabled, e.g. disallowing certain syntactically valid email addresses that are rejected by Gmail. If `blacklisted_chars` receives a string, then the validator will reject emails that include any of the characters in the string, in the name part. If `host_blacklist` is set to an array of strings or regexp, and the part of the email after the `@` symbol matches one of the strings defined in it, the validation fails. If `host_whitelist` is set to an array of strings or regexp, and the part of the email after the `@` symbol matches none of the strings defined in it, the validation fails.
 **isEmpty(str [, options])**            | check if the string has a length of zero.<br/><br/>`options` is an object which defaults to `{ ignore_whitespace: false }`.