Add from-scratch Windows installation instructions

doc/windows.md

+## Steps to install Arduino ESP32 support on Windows
+### Tested on 32 and 64 bit Windows 10 machines
+
+1. Download and install latest Arduino Windows Installer from [arduino.cc](https://www.arduino.cc/en/Main/Software)
+2. Download ```Windows x86 MSI installer``` or ```Windows x86-64 MSI installer``` from [python.org](https://www.python.org/downloads/release/python-2712/)
+    When installing:
+    - Install for all users
+    - In ```Customize Python 2.7.X``` page, make sure you enable the last option: ```Add python.exe to Path```
+    ![Python](python-install.png)
+3. Download and install Git from [git-scm.com](https://git-scm.com/download/win)
+4. Start ```Git Bash``` as Administrator and execute the following command
+```bash
+python -m pip install --upgrade pip && \
+pip install pyserial
+```
+ ![Git Bash As Admin](gitbash-admin-start.png)
+ ![Git Bash Admin CMD](gitbash-admin.png)
+
+5. Start ```Git Bash``` normally and execute the following command
+```bash
+mkdir -p ~/Documents/Arduino/hardware/espressif && \
+cd ~/Documents/Arduino/hardware/espressif && \
+git clone https://github.com/espressif/arduino-esp32.git esp32 && \
+cd esp32/tools/ && \
+python get.py
+```
+ ![Git Bash User CMD](gitbash-user.png)
+ 
+6. Plug your ESP32 board and wait for the drivers to install (or install manually any that might be required)
+7. Start Arduino IDE
+8. Select your board in ```Tools > Board``` menu
+9. Select the COM port that the board is attached to
+10. Compile and upload
+ ![Arduino IDE Example](arduino-ide.png)