Update README about FJSPLIB format

Author: leonlan

README.md

@@ -1,7 +1,27 @@
+> [!NOTE]
+> This package is under development. Expect things to break significantly during the v0.0.x phase.
+
+
 # FJSPLIB
 ![PyPI](https://img.shields.io/pypi/v/FJSPLIB?style=flat-square)
 ![License](https://img.shields.io/pypi/l/FJSPLIB?style=flat-square)
 ![CI](https://img.shields.io/github/actions/workflow/status/leonlan/FJSPLIB/.github%2Fworkflows%2FCI.yml?style=flat-square)
 ![Codecov](https://img.shields.io/codecov/c/github/leonlan/FJSPLIB?style=flat-square)
 
 FJSPLIB is a Python package for reading and writing flexible job shop problem (FJSP) instances.
+
+The FJSPLIB format is as follows:
+
+``` sh
+<num jobs> <num machines> <average operations per job>
+<num operations> * (<num machines> * (<machine idx> <duration>))
+...
+```
+
+The first line contains data about the number of jobs, number machines and average number of operations per job.
+The following lines each represent the job data, one line for each job.
+These lines are each parsed as follows:
+- The first number denotes the number of operations for this job.
+- Then, for each operation, the first number represents the number of machines that can process this operation, followed by the machine index and processing time for each eligible machine.
+
+The FJSPLIB format is not well-defined for extensions of the FJSP, such as sequence-dependent setup times and arbitrary precedence graphs. One goal of this project is to extend FJSPLIB format to include these and other variants.