Update instructions to apply to Guile

Also rename `main` to `main.lua` and `main.scm` to `main`.

1 files changed, 9 insertions, 3 deletions

diff --git a/README.md b/README.md
index e2c5cc5..0c29b03 100644
--- a/README.md
+++ b/README.md
@@ -1,16 +1,22 @@
 # Advent of code 2024
 
-These are my solutions for Advent of Code in 2024.  This year I'm using Lua as the programming language.  To launch the program for a given day, run
+These are my solutions for Advent of Code in 2024.  This year I'm using Guile
+Scheme as the programming language.  To launch the program for a given day, run
 
 ```sh
 ./main <<ID>> [<<FILE>>]
 ```
 
-where `<<ID>>` is the day number followed by `a` for the first part or `b` for the second part.  If the file is not specified, it defaults to the number of the day with two digits and extension `.in`, i.e. `01.in`.  One can use the name of a file that doesn't exist, e.g. `-`, to read from standard input.
+where `<<ID>>` is the day number followed by `a` for the first part or `b` for
+the second part.  If the file is not specified, it defaults to the number of the
+day with two digits and extension `.in`, i.e. `01.in`.  To read from standard
+input, use `-` as the file name.
 
 Example:
 
 ```sh
-./main 01b input
+./main 05b -
 ```
 
+Some of the first days are written in Lua rather than Guile Scheme.  To run
+them, simply replace `main` with `main.lua`.