Add install instructions

INSTALL.md

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+# Installation Guide
+
+This guide explains how to install the **ROCKNIX-ABL** custom Qualcomm ABL using **fastboot**.
+
+:warning: **Warning**: Flashing a custom ABL is risky and can permanently brick your device if done incorrectly. Proceed only if you understand the risks and have recovery options available.
+
+---
+
+## Requirements
+
+Before you begin, ensure you have the following:
+
+* A supported **Qualcomm-based device**
+* A **USB cable**
+* A PC running **Windows, Linux or macOS**
+* The correct **`abl_signed-SMXXXX.elf`** file for your device
+* Fastboot installed and working
+* Proper USB drivers installed (Windows users)
+
+---
+
+## Step 1: Install Fastboot & Drivers
+
+### Windows
+
+1. Download **Android Platform Tools** from Google
+2. Extract the archive
+3. Install the appropriate **USB drivers** for your device
+4. Ensure `fastboot.exe` is accessible from your command prompt
+
+### Linux
+
+Most distributions include fastboot in their package repositories:
+
+```bash
+sudo apt install android-tools-fastboot
+```
+
+(or equivalent for your distro)
+
+### macOS
+
+Using Homebrew:
+
+```bash
+brew install android-platform-tools
+```
+
+---
+
+## Step 2: Reboot Device into Fastboot Mode
+
+Power off your device completely.
+
+Boot into **fastboot mode** using one of the following methods:
+
+* **Hold Power + Volume Down** until fastboot mode appears
+* **Or from Android with USB debugging enabled:**
+
+```bash
+adb reboot bootloader
+```
+
+Verify the device is detected:
+
+```bash
+fastboot devices
+```
+
+---
+
+## Step 3: Flash the ABL
+
+From the directory containing the ABL file, run:
+
+```bash
+fastboot flash abl abl_signed-SMXXXX.elf
+```
+
+Wait for the flash process to complete successfully.
+
+---
+
+## Step 4: Reboot
+
+Once flashing is complete, reboot your device:
+
+```bash
+fastboot reboot
+```
+
+Your device should now boot using **ROCKNIX-ABL**.
+
+---
+
+## Notes
+
+* The default boot mode is **Linux**
+* Hold **Volume Up** during boot to force **Android**
+* Hold **Volume Down** during boot to enter **ROCKNIX-ABL**
+
+---
+
+## Support
+
+This project is provided **as-is**.
+
+For issues, feedback, or testing reports, please contact the **ROCKNIX Team** through our [#abl](https://discord.com/channels/948029830325235753/1458147167830020127) Discord channel.
+
+Happy gaming! :video_game::fire: