Add notes that matrix-appservice-slack is not available for new installation

The bridge uses a classic Slack application, but its creation has been discontinued since June 4, 2024.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-bridge-appservice-slack.md

@@ -1,6 +1,8 @@
 # Setting up Appservice Slack bridging (optional)
 
-**Note**: bridging to [Slack](https://slack.com) can also happen via the [mx-puppet-slack](configuring-playbook-bridge-mx-puppet-slack.md) and [mautrix-slack](configuring-playbook-bridge-mautrix-slack.md) bridges supported by the playbook.
+**Notes**:
+- Bridging to [Slack](https://slack.com) can also happen via the [mx-puppet-slack](configuring-playbook-bridge-mx-puppet-slack.md) and [mautrix-slack](configuring-playbook-bridge-mautrix-slack.md) bridges supported by the playbook.
+- Currently (as of November, 2024) this component is not available for new installation unless you have already created a classic Slack application (which the bridge makes use of in order to enable bridging between Slack and Matrix), because the creation of classic Slack applications has been discontinued since June 4 2024. The author of the bridge claims [here](https://github.com/matrix-org/matrix-appservice-slack/issues/789#issuecomment-2172947787) that he plans to support the modern Slack application and until then "the best (and only) option for new installations is to use the webhook bridging". The playbook supports the Webhook with [matrix-hookshot](configuring-playbook-bridge-hookshot.md). While the playbook supports `matrix-appservice-webhooks`, it has been deprecated in favor of matrix-hookshot.
 
 The playbook can install and configure [matrix-appservice-slack](https://github.com/matrix-org/matrix-appservice-slack) for you.
 

docs/configuring-playbook-bridge-mautrix-slack.md

@@ -1,7 +1,7 @@
 # Setting up Mautrix Slack bridging (optional)
 
 **Note**: bridging to [Slack](https://slack.com/) can also happen via the [mx-puppet-slack](configuring-playbook-bridge-mx-puppet-slack.md) and [matrix-appservice-slack](configuring-playbook-bridge-appservice-slack.md) bridges supported by the playbook.
-- For using as a Bot we recommend the [Appservice Slack](configuring-playbook-bridge-appservice-slack.md), because it supports plumbing.
+- For using as a Bot we recommend the [Appservice Slack](configuring-playbook-bridge-appservice-slack.md), because it supports plumbing. Note that it is not available for new installation unless you have already created a classic Slack application, because the creation of classic Slack applications, which this bridge makes use of, has been discontinued.
 - For personal use with a slack account we recommend the `mautrix-slack` bridge (the one being discussed here), because it is the most fully-featured and stable of the 3 Slack bridges supported by the playbook.
 
 The playbook can install and configure [mautrix-slack](https://github.com/mautrix/slack) for you.

docs/configuring-playbook-bridge-mx-puppet-slack.md

@@ -1,7 +1,6 @@
 # Setting up MX Puppet Slack bridging (optional)
 
-**Note**: bridging to [Slack](https://slack.com) can also happen via the
-[matrix-appservice-slack](configuring-playbook-bridge-appservice-slack.md) and [mautrix-slack](configuring-playbook-bridge-mautrix-slack.md) bridges supported by the playbook.
+**Note**: bridging to [Slack](https://slack.com) can also happen via the [matrix-appservice-slack](configuring-playbook-bridge-appservice-slack.md) and [mautrix-slack](configuring-playbook-bridge-mautrix-slack.md) bridges supported by the playbook. Note that `matrix-appservice-slack` is not available for new installation unless you have already created a classic Slack application, because the creation of classic Slack applications, which this bridge makes use of, has been discontinued.
 
 The playbook can install and configure [mx-puppet-slack](https://gitlab.com/mx-puppet/slack/mx-puppet-slack) for you.