Update README with installation and usage instructions

- Add comprehensive README with project overview
- Include installation steps using git clone and package instantiation
- Provide usage example demonstrating forward substitution
- Showcase library functionality with a simple code snippet

Author: yangjunjie0320

README.md

@@ -2,3 +2,30 @@
 
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+
+This is a simple linear algebra library that builds upon `julia` language.
+
+## Installation
+
+```bash
+git clone https://github.com/yangjunjie0320/SimpleLinearAlgebra.jl
+cd SimpleLinearAlgebra.jl
+julia --project=. -e 'using Pkg; Pkg.instantiate()'
+```
+
+## Usage
+
+```julia
+using LinearAlgebra
+using SimpleLinearAlgebra
+
+# forward substitution
+l = tril(rand(10, 10))
+b = rand(10)
+prob = ForwardSubstitution(l, b)
+soln = kernel(prob)
+
+x = soln.x
+@assert isapprox(l * x, b, atol=1e-10)
+```
+