kernelscript: add a little detailed instructions

The README.md was missing a couple of steps that are required when
bootstrapping a new system that hasn't built opam before.

I had to add the steps in order for my setup to work, hope this can help
others as well. I was building on Debian Trixie.

Signed-off-by: Jesse Brandeburg <jbrandeburg@cloudflare.com>

Author: jbrandeb

README.md

@@ -329,14 +329,15 @@ sudo ./my_project          # Run the program
 1. **Install system dependencies (Debian/Ubuntu):**
    ```bash
    sudo apt update
-   sudo apt install libbpf-dev libelf-dev zlib1g-dev
+   sudo apt install libbpf-dev libelf-dev zlib1g-dev opam bpftool
    ```
 
 2. **Install KernelScript:**
    ```bash
    git clone https://github.com/multikernel/kernelscript.git
    cd kernelscript
-   opam install . --deps-only
+   opam init
+   opam install . --deps-only --with-test
    eval $(opam env) && dune build && dune install
    ```
 
@@ -403,4 +404,4 @@ limitations under the License.
 
 ## Contributing
 
-By contributing to this project, you agree that your contributions will be licensed under the Apache License 2.0.
+By contributing to this project, you agree that your contributions will be licensed under the Apache License 2.0.