✏️ improve README

README.md

@@ -32,7 +32,16 @@ $ pip install jupyter
 $ opam install jupyter
 ```
 
-which will automatically register the kernel to Jupyter.
+which will automatically register the kernel to Jupyter if `jupyter` command is found.
+Otherwise (i.e., the command is not found in `$PATH`, or you have not installed Jupyter yet)
+you need to manually install the kernel:
+
+```console
+$ jupyter kernelspec install --name ocaml-jupyter "$(opam config var share)/ocaml-jupyter"
+[InstallKernelSpec] Removing existing kernelspec in /home/USERNAME/.local/share/jupyter/kernels/ocaml-jupyter
+[InstallKernelSpec] Installed kernelspec ocaml-jupyter-4.04.2 in /home/USERNAME/.local/share/jupyter/kernels/ocaml-jupyter
+```
+
 After installation, you can use `ocaml-jupyter` kernel by launching Jupyter notebook server:
 
 ```console
@@ -104,8 +113,6 @@ See `ocaml-jupyter-kernel --help` for details of command-line parameters in `arg
 
 ```console
 $ jupyter kernelspec install --name ocaml-jupyter "$(opam config var share)/ocaml-jupyter"
-[InstallKernelSpec] Removing existing kernelspec in /home/USERNAME/.local/share/jupyter/kernels/ocaml-jupyter-4.04.2
-[InstallKernelSpec] Installed kernelspec ocaml-jupyter-4.04.2 in /home/USERNAME/.local/share/jupyter/kernels/ocaml-jupyter-4.04.2
 ```
 
 ## Related work