chore(sbat): add note about alignment of sbat.csv

src/sbat.rs

@@ -3,6 +3,9 @@ const SBAT_SIZE: usize = 512;
 
 /// Define the SBAT attestation by including the sbat.csv file.
 /// See this document for more details: https://github.com/rhboot/shim/blob/main/SBAT.md
+/// NOTE: Alignment can't be enforced by an attribute, so instead the alignment is currently
+/// enforced by the SBAT_SIZE being 512. The build.rs will ensure that the sbat.csv is padded.
+/// This code will not compile if the sbat.csv is a different size than SBAT_SIZE.
 #[used]
 #[unsafe(link_section = ".sbat")]
 static SBAT: [u8; SBAT_SIZE] = *include_bytes!(concat!(env!("OUT_DIR"), "/sbat.csv"));