Add mapping example to README (#70)

* Add mapping example to README

* move to FAQ section

README.md

@@ -165,7 +165,6 @@ mapping = {
 }
 ```
 
-
 #### completion.autocomplete (type: cmp.TriggerEvent[])
 
 Which events should trigger `autocompletion`.
@@ -335,6 +334,50 @@ The `cmp-buffer` source makes index of the current buffer so if the current buff
 For example, `typescript-language-server` will returns 15k items to the client.
 In such case, the time near the 100ms will be consumed just to parse payloads as JSON.
 
+#### How to setup supertab-like mapping?
+
+This is supertab-like mapping for [LuaSnip](https://github.com/L3MON4D3/LuaSnip)
+
+```lua
+local t = function(str)
+  return vim.api.nvim_replace_termcodes(str, true, true, true)
+end
+local check_back_space = function()
+  local col = vim.fn.col '.' - 1
+  return col == 0 or vim.fn.getline('.'):sub(col, col):match '%s' ~= nil
+end
+local luasnip = require("luasnip")
+
+-- supertab-like mapping
+mapping = {
+  ["<tab>"] = cmp.mapping(function(fallback)
+    if vim.fn.pumvisible() == 1 then
+      vim.fn.feedkeys(t("<C-n>"), "n")
+    elseif luasnip.expand_or_jumpable() then
+      vim.fn.feedkeys(t("<Plug>luasnip-expand-or-jump"), "")
+    elseif check_back_space() then
+      vim.fn.feedkeys(t("<tab>"), "n")
+    else
+      fallback()
+    end
+  end, {
+    "i",
+    "s",
+  }),
+  ["<S-tab>"] = cmp.mapping(function(fallback)
+    if vim.fn.pumvisible() == 1 then
+      vim.fn.feedkeys(t("<C-p>"), "n")
+    elseif luasnip.jumpable(-1) then
+      vim.fn.feedkeys(t("<Plug>luasnip-jump-prev"), "")
+    else
+      fallback()
+    end
+  end, {
+    "i",
+    "s",
+  }),
+}
+```
 
 Source creation
 ====================