Add initialization and build instructions to AGENTS.md (#166)

Added instructions for initializing and building the repository for agents

AGENTS.md

@@ -0,0 +1,14 @@
+# To initialize the repository:
+
+Run these commands from the project directory.
+
+```shell
+./configure && touch src/.accepted  # the src/.accepted file must exist to build.
+```
+
+# To build the code:
+
+```shell
+cd src     # make must be run from the src dir
+make       # builds all changed source files.
+```