doc: troubleshooting: add procedure to clear shaarli caches

doc/md/Server-configuration.md

@@ -202,6 +202,7 @@ systemctl restart apache
 
 See [How to install the Apache web server](https://www.digitalocean.com/community/tutorials/how-to-install-the-apache-web-server-on-debian-10) for a complete guide.
 
+
 ### Nginx
 
 This examples uses nginx and the [PHP-FPM](https://www.digitalocean.com/community/tutorials/how-to-install-linux-nginx-mariadb-php-lemp-stack-on-debian-10#step-3-%E2%80%94-installing-php-for-processing) PHP interpreter. Nginx and PHP-FPM must be running using the same user and group, here we assume the user/group to be `www-data:www-data`.

doc/md/Troubleshooting.md

@@ -176,6 +176,16 @@ Under Opera, you can't drag'n drop the button: You have to right-click on it and
 - A new date/time field becomes available in the edit/new Shaare dialog.
 - You can set the timestamp manually by entering it in the format `YYYMMDD_HHMMS`.
 
+### Clearing Shaarli caches
+
+For debugging purposes:
+
+```bash
+# clear raintpl cache and temporary files
+find /var/www/links/cache/ /var/www/links/pagecache/ /var/www/links/tmp/ -type f -exec rm -v '{}' \;
+# if you have a php accelerator such as php-apcu, restart the webserver
+sudo systemctl restart apache2
+```
 
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