Created Server Query Protocol (markdown)

Server-Query-Protocol.md

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+This only applies to the `port-net` branch.
+
+It is possible to query game information from the server without connecting to it. This is done by sending a special UDP packet to the server, to the same port that is used for the game itself. For a basic example in Python, check out [this script](https://github.com/fgsfdsfgs/perfect_dark/blob/port-net/tools/query.py).
+
+### Request packet
+
+`"PDQM\x01"` (bytes `50 44 51 4D 01`)
+
+### Response packet
+
+```
+struct {
+  char magic[5] = "PDQM\x01"; // same as query
+  u16 size;                   // total size of this packet
+  u32 protocol                // protocol version (NET_PROTOCOL_VER)
+  u8 flags;                   // currently just 1 if game is in progress and 0 otherwise
+  u8 numclients;              // currently connected clients
+  u8 maxclients;              // max connected clients
+  u8 stagenum;                // current stage number (see stagetable.txt)
+  u8 scenario;                // combat sim scenario
+  dstring hostname;           // nickname of hosting player
+  dstring romname;            // ROM file name
+  dstring moddir;             // mod directory if a mod is loaded, empty string otherwise
+  u16 checksum;               // checksum of all the packet data before this point
+};
+```
+where `dstring` is
+```
+u16 length;        // including null terminator
+char data[length]; // null terminated
+```
+The checksum function used is as follows:
+```
+u32 chk = 1;
+for (u32 i = 0; i < datalen; ++i) {
+  chk = (chk + data[i]) % 65521;
+}
+```