docs: Add skeletal developer document

Signed-off-by: James O. D. Hunt <[email protected]>

README-DEVELOPER.md

@@ -0,0 +1,18 @@
+# procenv developer details
+
+> **Note:**
+>
+> This document assumes you have already read the
+> [build document](README-BUILD.md).
+
+## Debug with gdb or lldb
+
+To disable optimisations when building `procenv`, configure by specifying
+the `--disable-compiler-optimisations` configure option (which sets the
+`-O0` compiler option):
+
+```bash
+$ /configure --disable-compiler-optimisations
+$ make
+$ gdb src/procenv
+```

README.md

@@ -141,6 +141,10 @@ applications.
 For instructions on building from source, see also the
 [build document](README-BUILD.md).
 
+## Developer documentation
+
+See the [developer document](README-DEVELOPER.md).
+
 ## Install
 
 ### Snap