Add OS icons for Irssi and Weechat

I'm not adding them for glirc or BitchX, because their
websites are (respectively) not providing the info and broken.

Author: progval

_data/sw_clients.yml

@@ -174,6 +174,11 @@
     - name: Irssi
       # ref: https://github.com/irssi/irssi/blob/8a5d5d384ed20cefa3fdc4a65d27fac3e4913a7b/src/irc/core/irc-servers.h#L17
       link: https://irssi.org
+      os:
+        - bsd
+        - linux
+        - macos
+        - windows
       support:
         stable:
           account-notify: Git
@@ -398,6 +403,10 @@
       # ref: https://weechat.org/files/changelog/ChangeLog-devel.html or IRC_COMMAND_CAP_SUPPORTED_COMPLETION
       # in https://github.com/weechat/weechat/blob/v3.1/src/plugins/irc/irc-command.h
       link: https://weechat.org
+      os:
+        - bsd
+        - linux
+        - macos
       support:
         stable:
           account-notify: