updated readme, and fixed linux compilation

README.md

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+# External Merge Sort (Big Buffer Strategy)
+A C++20 implementation of an external sorting algorithm designed to sort files that are too large to fit into the system's RAM. This project uses a Big Buffer approach to minimize disk I/O by maximizing the use of available memory during both the initial run creation and the merging phases.
+
+# Requirements
+  Clang++ or G++ (Support for C++20 required)
+  Make
+  
+# Compilation
+```bash
+make
+````
+
+# Usage
+
+The binary is located in the build/ directory after compilation.
+
+# Generate Data
+
+# To generate a test file with 100,000 random records:
+```bash
+./build/main -g 100000 -o input.dat
+```
+
+# Sort Data
+
+To sort the generated file using 11 buffers of 10 records each:
+```bash
+./build/main -i input.dat -o output.dat -n 11 -b 10
+```
+
+# Options
+Flag	Description
+-i	Input file path
+-o	Output file path
+-n	Number of buffers (minimum 3)
+-b	Size of each buffer (number of records)
+-g	Generate count random records
+-e	Evaluate and print the contents of a file
+-d	Temporary directory for merge runs