craft-doc: say what the total budget counts

The max_total and Budget docs now say the budget counts bytes consumed
from gzip, and that unused lookahead from the initial gzip read (chunks
of up to 64 KiB) is not counted.

crates/doc/src/lib.rs

@@ -134,9 +134,10 @@ pub struct Limits {
     pub max_json: u64,
     /// Most bytes of one rendition or one ZIP entry. Default 256 MiB.
     pub max_entry: u64,
-    /// Most bytes one call decompresses from gzip, reads out of ZIP entries and returns as
+    /// Most bytes one call consumes from gzip, reads out of ZIP entries and returns as
     /// renditions, together; a rendition decompressed from gzip is counted once, and a second
-    /// rendition of the same bytes as another copy. Default 1 GiB.
+    /// rendition of the same bytes as another copy. Unused lookahead from initial gzip reads
+    /// (chunks of up to 64 KiB) is not counted. Default 1 GiB.
     pub max_total: u64,
     /// Deepest nesting of JSON arrays and objects, at most [`MAX_DEPTH`] (a larger value counts
     /// as [`MAX_DEPTH`]). Default [`MAX_DEPTH`]. [`renditions`] and [`outline`] also refuse a
@@ -313,7 +314,7 @@ fn malformed(m: impl std::fmt::Display) -> Error {
     Error::Malformed(m.to_string())
 }
 
-/// The bytes one call may still decompress, read out of ZIP entries or return as renditions.
+/// The bytes one call may still consume from gzip or ZIP entries, or return as renditions.
 pub(crate) struct Budget<'a> {
     pub(crate) limits: &'a Limits,
     left: u64,