Clearly document behaviour when end of file is reached.

Closes #260.
diff --git a/man/zip_fread.mdoc b/man/zip_fread.mdoc
index 4d3e8d6..48166b7 100644
--- a/man/zip_fread.mdoc
+++ b/man/zip_fread.mdoc
@@ -29,7 +29,7 @@
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 .\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd December 18, 2017
+.Dd September 28, 2021
 .Dt ZIP_FREAD 3
 .Os
 .Sh NAME
@@ -44,7 +44,7 @@
 .Sh DESCRIPTION
 The
 .Fn zip_fread
-function reads at most
+function reads up to
 .Ar nbytes
 bytes from
 .Ar file
@@ -52,7 +52,10 @@
 .Ar buf .
 .Sh RETURN VALUES
 If successful, the number of bytes actually read is returned.
-Otherwise, \-1 is returned.
+When
+.Fn zip_fread
+is called after reaching the end of the file, 0 is returned.
+In case of error, \-1 is returned.
 .Sh SEE ALSO
 .Xr libzip 3 ,
 .Xr zip_fclose 3 ,
diff --git a/man/zip_source_read.mdoc b/man/zip_source_read.mdoc
index 1e7bc02..c0fa37d 100644
--- a/man/zip_source_read.mdoc
+++ b/man/zip_source_read.mdoc
@@ -29,7 +29,7 @@
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 .\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd December 18, 2017
+.Dd September 28, 2021
 .Dt ZIP_SOURCE_READ 3
 .Os
 .Sh NAME
@@ -58,7 +58,9 @@
 first.
 .Sh RETURN VALUES
 Upon successful completion the number of bytes read is returned.
-Upon reading end-of-file, zero is returned.
+When
+.Fn zip_source_read
+is called after reaching the end of the file, 0 is returned.
 Otherwise, \-1 is returned and the error information in
 .Ar source
 is set to indicate the error.