doc: Server Requirements: php-mbstring: add 'hosting providers'

doc/md/Server-requirements.md

@@ -35,7 +35,7 @@ Library | Required? | Usage
 Extension | Required? | Usage
 ---|:---:|---
 [`openssl`](http://php.net/manual/en/book.openssl.php) | All | OpenSSL, HTTPS
-[`php-mbstring`](http://php.net/manual/en/book.mbstring.php) | CentOS, Fedora, RHEL, Windows | multibyte (Unicode) string support
+[`php-mbstring`](http://php.net/manual/en/book.mbstring.php) | CentOS, Fedora, RHEL, Windows, some hosting providers | multibyte (Unicode) string support
 [`php-gd`](http://php.net/manual/en/book.image.php) | optional | thumbnail resizing
 [`php-intl`](http://php.net/manual/en/book.intl.php) | optional | localized text sorting (e.g. `e->è->f`)
 [`php-curl`](http://php.net/manual/en/book.curl.php) | optional | using cURL for fetching webpages and thumbnails in a more robust way