add all initial steps to readme for windows

windows_cygwin/README.md

@@ -1,4 +1,19 @@
 Bootstrap from cmd.exe running as Administrator:
 
-    bootstrap.bat
+    @powershell -NoProfile -ExecutionPolicy Bypass -Command "iex ((New-Object System.Net.WebClient).DownloadString('https://raw.githubusercontent.com/cyplo/dotfiles/master/windows_cygwin/bootstrap.ps1'))"
+
+launch a normal user's cmd.exe and:
+
+    refreshenv
     ssh-keygen -b 8192
+    type .ssh\id_rsa.pub
+    # add this key to github
+    mkdir dev
+    cd dev
+    git clone git@github.com:cyplo/dotfiles.git
+
+launch new cmd.exe as Administrator and:
+    
+    cd %HOMEPATH%\dev\dotfiles
+    windows_cygwin\build.bat
+