Update docs for OCaml 5.4 (#566)

* Update docs for OCaml 5.4

This is to reflect the update to the test runner in
exercism/ocaml-test-runner#68.

* Update Docker image to OCaml 5.4

This is to match the version used by the test runner.

Author: kahgoh

.github/Dockerfile

@@ -1,4 +1,4 @@
-FROM ocaml/opam:debian-11-ocaml-5.1-afl
+FROM docker.io/ocaml/opam:debian-13-ocaml-5.4-no-flat-float-array
 
 USER root
 
@@ -33,5 +33,5 @@ RUN opam update \
     getopt \
     stdio
 
-ENV PATH="/home/opam/.opam/5.1/bin:${PATH}" \
-    MAKESYSPATH=/usr/share/bmake/mk-bmake
+ENV PATH="/home/opam/.opam/5.4/bin:${PATH}" \
+    MAKESYSPATH=/usr/share/bmake/mk-bmake

README.md

@@ -15,7 +15,7 @@ notes contain a few details specific to Ocaml.
 
 **Prerequisites**
 
-- OCaml `5.1`
+- OCaml `5.4`
 - opam
 - make
 

docs/INSTALLATION.md

@@ -18,7 +18,7 @@ To work on the exercises, you will need these pieces of software:
    If you already have a switch for OCaml 5.1, either load that by running `opam switch <switch-name>`, or create a new switch by running:
 
    ```bash
-   opam switch create exercism 5.1.1
+   opam switch create exercism 5.4.0
    ```
 
    The name `exercism` here is optional, but naming your switches is a good practice.