doc: add explanation of php-json requirement

diff --git a/doc/md/Server-configuration.md b/doc/md/Server-configuration.md
index b9ac01cb3f19e2aaf53eb04b6a704f5e5a2f498c..bd293c37919e47a24dbec6a3bf1c92db595fdff7 100644 (file)
--- a/doc/md/Server-configuration.md
+++ b/doc/md/Server-configuration.md
@@ -28,7 +28,7 @@ Version | Status | Shaarli compatibility
 Extension | Required? | Usage
 ---|:---:|---
 [`openssl`](http://php.net/manual/en/book.openssl.php) | All | OpenSSL, HTTPS
-[`php-json`](http://php.net/manual/en/book.json.php) | required | ?
+[`php-json`](http://php.net/manual/en/book.json.php) | required | configuration parsing
 [`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 | required to use thumbnails
 [`php-intl`](http://php.net/manual/en/book.intl.php) | optional | localized text sorting (e.g. `e->è->f`)