Add protocol version documentation

docs/protocol-version.md

@@ -0,0 +1,39 @@
+# Protocol version
+
+The Minecraft protocol uses a version number to distinguish between different
+protocol versions. Each new Minecraft version having a change in its protocol
+gets a new protocol version.
+
+## List of versions
+
+- https://wiki.vg/Protocol_version_numbers#Versions_after_the_Netty_rewrite
+
+## Configuration
+
+In `lazymc` you may configure what protocol version to use:
+
+[`lazymc.toml`](../res/lazymc.toml):
+
+```bash
+# -- snip --
+
+[public]
+# Server version & protocol hint.
+# Sent to clients until actual server version is known.
+# See: https://git.io/J1Fvx
+version = "1.17.1"
+protocol = 756
+
+# -- snip --
+```
+
+It is highly recommended to set these to match that of your server version to
+allow the best compatibility with clients.
+
+- Set `public.protocol` to the number matching that of your server version
+  (see [this](#list-of-versions) list)
+- Set `public.version` to any string you like. Shows up in read in clients that
+  have an incompatibel protocol version number
+
+These are used as hint. `lazymc` will automatically use the protocol version of
+your Minecraft server once it has started at least once.