docs: Search domains (#8437)

- Adds search domains section to Deploy -> DNS docs
- Mentions known issue: #8430

website/src/app/kb/client-apps/android-client/readme.mdx

@@ -93,6 +93,7 @@ We will add troubleshooting steps here in the future.
 
 ## Known issues
 
-None at this time.
+- If a search domain is applied, the system search domains set manually or by
+  DHCP are ignored. [#8430](https://github.com/firezone/firezone/issues/8430).
 
 <SupportOptions />

website/src/app/kb/client-apps/linux-gui-client/readme.mdx

@@ -86,8 +86,8 @@ already work properly.
 
 ### Signing in
 
-1. Start the GUI by running `Firezone Client` from your desktop
-   environment's application menu or from an interactive shell.
+1. Start the GUI by running `Firezone Client` from your desktop environment's
+   application menu or from an interactive shell.
 1. At the Welcome screen, click `Sign in`. This will open the Firezone sign-in
    page in your default web browser.
 1. Sign in using your account slug and identity provider
@@ -260,5 +260,7 @@ the tunnel, and a GUI which allows the user to control Firezone.
   [#7646](https://github.com/firezone/firezone/issues/7646)
 - If you update Firezone while the GUI is running, you must manually restart the
   GUI [#5790](https://github.com/firezone/firezone/issues/5952)
+- If a search domain is applied, the system search domains set manually or by
+  DHCP are ignored. [#8430](https://github.com/firezone/firezone/issues/8430).
 
 <SupportOptions />

website/src/app/kb/client-apps/linux-headless-client/readme.mdx

@@ -264,6 +264,7 @@ sudo mv /etc/resolv.conf.before-firezone /etc/resolv.conf
 
 ## Known issues
 
-None at this time.
+- If a search domain is applied, the system search domains set manually or by
+  DHCP are ignored. [#8430](https://github.com/firezone/firezone/issues/8430).
 
 <SupportOptions />

website/src/app/kb/client-apps/windows-gui-client/readme.mdx

@@ -212,6 +212,8 @@ the tunnel, and a GUI which allows the user to control Firezone.
 
 ## Known issues
 
+- If a search domain is applied, DNS suffix search list of other adapters are
+  ignored. [#8430](https://github.com/firezone/firezone/issues/8430).
 - Firezone does not register itself with Windows as a VPN
   [#2875](https://github.com/firezone/firezone/issues/2875)
 - The Windows client is not yet available for Arm64 devices

website/src/app/kb/client-apps/windows-headless-client/readme.mdx

@@ -207,6 +207,8 @@ Get-DnsClientNrptRule | where Comment -eq firezone-fd0020211111 | foreach { Remo
 
 ## Known issues
 
+- If a search domain is applied, DNS suffix search list of other adapters are
+  ignored. [#8430](https://github.com/firezone/firezone/issues/8430).
 - The Windows client is not yet available for Arm64 devices
   [#2992](https://github.com/firezone/firezone/issues/2992)
 

website/src/app/kb/deploy/dns/readme.mdx

@@ -84,6 +84,24 @@ resolver(s).
 
 </Alert>
 
+## Configuring search domains
+
+A search domain (sometimes known as a default DNS suffix) can be configured with
+the domain name of your choosing in the `Settings -> DNS` page. This domain will
+automatically be appended to **all single-label queries on the system** when a
+Client device is signed into Firezone.
+
+<Alert color="warning">
+
+On Apple devices, the search domain set in the Firezone admin portal is applied
+_in addition_ to any locally-configured search domains. On Android, Linux, and
+Windows devices, however, these are applied _instead of_ any locally-configured
+search domains. If this is causing an issue for your use case, please leave
+feedback on
+[this GitHub issue](https://github.com/firezone/firezone/issues/8430).
+
+</Alert>
+
 ## Configuring Client DNS upstream resolvers
 
 Upstream DNS in all Clients can be configured with the servers of your choosing