added README.md

README.md

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+# gm_sled
+
+gm_sled is really simple wrapper around [sled](https://github.com/spacejam/sled) key-value database.
+
+# Installation
+Download latest binary for corresponding OS and throw it into `garrysmod/lua/bin/`.  
+Or, you can compile your own version.
+
+Compilation for main Garry's Mod branch:
+```bash
+cargo build --release --target i686-unknown-linux-gnu
+```
+Compilation for x86-x64 branch:
+```bash
+cargo build --release --target x86_64-unknown-linux-gnu
+```
+
+# Example usage (but not really good example)
+```lua
+require("sled")
+
+local buffer = sled.Buffer(8)
+local db = sled.Open("currencydb")
+
+currencydb = {__currency = {}}
+
+function currencydb.set(player, currency, value)
+    local tree = currencydb.__currency[currency]
+    if not tree then
+        tree = db:OpenTree(currency)
+        currencydb.__currency[currency] = tree
+    end
+    -- In future, it will be done almost like in newer versions of lua.
+    -- Just like string.pack and string.unpack.
+    -- example: tree:InsertStruct(player:SteamID64(), "d", value)
+    buffer:Clear()
+    buffer:WriteDouble(value)
+    tree:Insert(player:SteamID64(), buffer:GetValue())
+end
+
+function currencydb.get(player, currency)
+    local tree = currencydb.__currency[currency]
+    if not tree then
+        tree = db:OpenTree(currency)
+        currencydb.__currency[currency] = tree
+    end
+    local data = tree:Get(player:SteamID64())
+    if not data then return 0 end
+    -- also: tree:GetStruct(player:SteamID64(), "d")
+    buffer:SetValue(data)
+    return buffer:ReadDouble()
+end
+
+function currencydb.list()
+    local names = {}
+    for name in db:TreeNames() do
+        if name == "__sled__default" then continue end
+        table.insert(names, name)
+    end
+    return names
+end
+```