Add doc for vscode

docs/vscode.md

+# Use Visual Studio Code on Chromium code base
+
+[Visual Studio Code](http://code.visualstudio.com/)
+([Wikipedia](https://en.wikipedia.org/wiki/Visual_Studio_Code)) is a
+multi-platform code editor that is itself based on Electron which is based on 
+Chromium. Visual Studio Code has a growing community and base of installable 
+extensions and themes. It works without too much setup.
+
+## Install extensions
+
+`ctrl+p` paste `ext install cpptools you-complete-me` then enter. 
+For more extensions: https://marketplace.visualstudio.com/search?target=vscode
+
+Highly recommend you also install your favorite keymap. 
+
+An Example to install eclipse keymaps `ext install vscode-eclipse-keybindings`. 
+You can search keymaps here. 
+https://marketplace.visualstudio.com/search?target=vscode&category=Keymaps
+
+
+## Settings
+
+Open Settings `File/Code - Preferences - Settings` and add the following 
+settings.
+
+```
+{
+  "editor.tabSize": 2,
+  "editor.rulers": [80],
+  // CPP
+  "C_Cpp.clang_format_path": "<your_depot_tools_path>/clang-format",
+  "C_Cpp.clang_format_fallbackStyle": "Chromium",
+  // Exclude
+  "files.exclude": {
+    "**/.git": true,
+    "**/.svn": true,
+    "**/.hg": true,
+    "**/.DS_Store": true,
+    "**/out": true
+  },
+  // YCM
+  "ycmd.path": "<your_ycmd_path>",
+  "ycmd.global_extra_config": 
+      "<your_chromium_path>/src/tools/vim/chromium.ycm_extra_conf.py",
+  "ycmd.confirm_extra_conf": false,
+  "ycmd.use_imprecise_get_type": true
+}
+```
+
+### Install auto-completion engine(ycmd)
+
+```
+$ git clone https://github.com/Valloric/ycmd.git ~/.ycmd
+$ cd ~/.ycmd
+$ ./build.py --clang-completer
+```
+
+## Work flow
+
+1. `ctrl+p` open file.
+2. `ctrl+shift+o` goto symbol. `ctrl+l` goto line.
+3. <code>ctrl+`</code> toggle terminal.
+
+## Tips
+
+### On laptop
+
+Because we use ycmd to enable auto completion. we can disable CPP autocomplete 
+to save battery. `"C_Cpp.autocomplete": "Disabled"`
+
+### More
+
+https://github.com/Microsoft/vscode-tips-and-tricks/blob/master/README.md