doc(ai4dev/README): add AI prompt instructions

Author: rouson

doc/ai4dev/README.md

@@ -0,0 +1,34 @@
+Set Up
+-----------
+With your present working directory set to `doc/ai4dev`, execute
+```bash
+cd  ../../scripts/
+./create-single-source-file-programs.sh 
+cd ../build/single-file-programs
+```
+
+Vibe Coding
+-----------
+1. Compile and execute `diffusion-app.F90` to ensure that the program
+   terminates normally.  For example, with the `gfortran` compiler,
+   run `gfortran -fcoarray=single -o diffusion-app diffusion-app.F90` 
+   followed by `./diffusion-app`.
+2. Edit `diffusion-app.F90` to remove the lines beginning and ending with 
+   `module procedure laplacian` and `end procedure laplacian`, respectively.
+3. Enter the file `doc/ai4dev/vibe-coding/README.md` as your prompt and
+   attach the edited `diffusion-app.F90` file.
+4. Insert the resulting function into the `subdomain_s` submodule and
+   try compiling and executing again to check the result.
+
+Idiomtic Vibe Coding
+--------------------
+1. Compile and execute `test-suite.F90` to and check that the output 
+   reports that all tests pass.  For example, with the `gfortran` compiler,
+   run `gfortran -fcoarray=single -o test-suite test-suite.F90` followed
+   by `./test-suite`.
+2. Edit `test-suite.F90` to remove the lines beginning and ending with 
+   `module procedure laplacian` and `end procedure laplacian`, respectively.
+3. Enter the file `doc/ai4dev/idiomaic-vibe-coding/README.md` as your prompt 
+   and attach the edited `tgest-sutie.F90` file.
+4. Insert the resulting function into the `subdomain_s` submodule and
+   try compiling and executing again to check the result.

src/matcha/subdomain_s.F90

@@ -142,7 +142,7 @@
 
     if (me==1) laplacian_rhs%s_(1,:,:) = 0. ! low-x boundary
     if (me==num_subdomains) laplacian_rhs%s_(my_nx,:,:) = 0. ! high-x boundary
-  end procedure
+  end procedure laplacian
 
   module procedure multiply
     call_assert(allocated(rhs%s_))