plugins: move description of weechat-plugin.h below the copyright and license

src/plugins/weechat-plugin.h

@@ -1,6 +1,4 @@
 /*
- * weechat-plugin.h - header to compile WeeChat plugins
- *
  * SPDX-FileCopyrightText: 2003-2025 Sébastien Helleu <flashcode@flashtux.org>
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
@@ -21,6 +19,8 @@
  * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/* The single header used to compile WeeChat plugins */
+
 #ifndef WEECHAT_WEECHAT_PLUGIN_H
 #define WEECHAT_WEECHAT_PLUGIN_H