Documentation: Move IPC endpoint documentation to manpage section 4

Base/usr/share/man/man4/ipc.md

@@ -0,0 +1,23 @@
+## Name
+
+ipc - Unix socket Inter Process Communication protocols
+
+## Synopsis
+
+IPC endpoints are provided as Unix sockets in `/tmp/portal`. All services have their own formats, automatically implemented through LibIPC.
+
+## Description
+
+The specifics of each service's format depend on the corresponding source `.ipc` file.
+
+The format can be identified by the format magic, which is derived in [`Meta/Lagom/Tools/CodeGenerators/IPCCompiler/main.cpp`](../../../../../Meta/Lagom/Tools/CodeGenerators/IPCCompiler/main.cpp) from the service-endpoint name, e.g. "ClipboardClient" (which hashes to 4008793515) or "ClipboardServer" (which hashes to 1329211611).
+
+In general, communication works by packets, which might have been sent in response to other packets. Everything is host endianness. Each packet consists of:
+- a 32-bit message size (see `Connection::try_parse_messages` in [`Userland/Libraries/LibIPC/Connection.h`](../../../../../Userland/Libraries/LibIPC/Connection.h))
+- the 32-bit endpoint magic (note that responses use the endpoint of the requesting packet, so the Clipboard server might use the endpoint magic 4008793515 to signal that this packet is a response)
+- the 32-bit message ID within that endpoint (sequentially assigned, starting at 1)
+- the data of that message itself (e.g. see `Messages::ClipboardServer::SetClipboardData::{en,de}code` in `Build/*/Userland/Services/Clipboard/ClipboardServerEndpoint.h`).
+
+## See Also
+
+- [ipc(5)](help://man/5/ipc) (IPC file format documentation)

Base/usr/share/man/man5/ipc.md

@@ -14,3 +14,4 @@ The format is loosely inspired by C++ headers.
 ## See Also
 
 - [`Meta/Lagom/Tools/CodeGenerators/IPCCompiler/`](../../../../../Meta/Lagom/Tools/CodeGenerators/IPCCompiler/).
+- [ipc(4)](help://man/4/ipc) (IPC Unix socket documentation)