add comment to clarify that orjson 3.9.10 vendors the Rust crates it requires in source tarball

Author: boegel

easybuild/easyconfigs/p/pymatgen/pymatgen-2023.12.18-foss-2023a.eb

@@ -84,6 +84,10 @@ exts_list = [
              'd299f388044fdcff32fc246b0215ae4b656bc20d9d3c759d545cbe3167df08b8'},
         ],
     }),
+    # note: this version of orjson vendors the required Rust crates in the source tarball
+    # under include/cargo (and instructs cargo to pick up on them via a custom .cargo/config.toml),
+    # so no list of crates needs to be specified in this easyconfig to prevent downloading
+    # crates by cargo during the installation
     ('orjson', '3.9.10', {
         'checksums': ['9ebbdbd6a046c304b1845e96fbcc5559cd296b4dfd3ad2509e33c4d9ce07d6a1'],
     }),