Add build instructions

Build.md

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+# Building
+
+## Running a developer build
+
+On every change made in this repository, [Github Actions](https://github.com/suchmememanyskill/CYD-Klipper/actions) automatically builds the firmware images for various screens. You can run one of these images as follows:
+
+#### Getting a firmware image
+0. Make sure you are logged into github
+1. Go to a [Github Actions](https://github.com/suchmememanyskill/CYD-Klipper/actions) build summary, then download the `firmware` Artifact.
+2. Open the firmware.zip archive you just downloaded, open the corresponding folder for your screen, then extract `merged_firmware.bin`
+
+This merged_firmware.bin file is a ready to flash image. Note that flashing this image does wipe your current configuration.
+
+#### Flashing merged_firmware.bin
+1. Download and extract [esptool](https://github.com/espressif/esptool/releases) to a new folder
+    - For windows, download `esptool-v4.7.0-win64.zip`
+2. Open a terminal window and navigate to this new folder containing esptool
+    - In windows, you can type cmd and press enter in the address bar in explorer to jump to the folder in cmd ![cmd](readme/cmd.jpg)
+3. Move `merged-firmware.bin` into this new folder
+4. Connect the display to your computer
+5. Execute the command `esptool write_flash 0x0 merged-firmware.bin`
+    - Don't forget to hold down the boot button on the display
+
+## Building via PlatformIO
+
+0. Install [Visual Studio Code](https://code.visualstudio.com/) and install the PlatformIO IDE plugin.
+1. Download the source code of CYD-Klipper
+    - This can be done via the `git clone https://github.com/suchmememanyskill/CYD-Klipper` command or via the green `<> Code` button on Github
+2. Open the CYD-Klipper folder inside the CYD-Klipper folder in Visual Studio Code
+3. Click on the Alien/Bug tab (PlatformIO) on the left
+4. Expand the folder/tab for your specific screen
+    - Entries with the suffix '-SD' are using the smartdisplay driver. Entries without this suffix are using a custom driver
+    - Usually, a custom driver is preferred over the smartdisplay driver
+5. Connect the display to your computer
+6. Click 'Upload and Monitor'
+    - This will start compiling the code, and after upload it to the display
+    - Don't forget to hold the boot button while flashing. The screen will flash when the firmware is attempted to be flashed