Create INSTALL_Linux.md

Author: TimGoTheCreator

INSTALL_Linux.md

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+# INSTALL_Linux.md
+
+# 🐧 Building NEXT on Linux (Ubuntu)
+
+## Prerequisites
+
+- Git
+- CMake ≥ 3.10
+- GCC or Clang
+- OpenMP
+- HDF5 development libraries
+- Python 3 (for input generation)
+
+## Steps
+
+1. **Clone the repository**
+
+```bash
+git clone https://github.com/TimGoTheCreator/NEXT.git
+cd NEXT
+```
+
+2. **Install dependencies**
+
+```bash
+sudo apt-get update
+sudo apt-get install -y libomp-dev libhdf5-dev python3
+```
+
+3. **Build NEXT**
+
+```bash
+mkdir build
+cd build
+cmake ..
+cmake --build . --config Release
+cd ..
+```
+
+4. **Run a built-in example simulation**
+
+```bash
+cd examples/TwoBodies
+python two_body.py
+../../next two_body.txt 8 0.01 0.1 vtu
+```
+
+5. **View results**
+
+Open the `.vtu` output in ParaView.