Update doc on deselect, file size

nnn.1

@@ -141,11 +141,17 @@ There are 3 groups of shortcuts to add files to selection:
 .br
 (3) add all files in the current directory to selection
 .Pp
-Repeat range selection on the same entry to clear selection. Selected files are visually indicated by a \fI+\fR before the entries.
+Selected files are visually indicated by a \fI+\fR before the entries.
 .br
 The selection can now be listed, copied, moved, removed, archived or linked.
 .br
 Absolute paths of the selected files are copied to the temporary file \fB.selection\fR in the config directory. The path is shown in the help and configuration screen. If \fB$NNN_COPIER\fR is set (see ENVIRONMENT section below) the file paths are also copied to the system clipboard.
+.Pp
+Repeat range selection on the same entry to clear selection. Deselecting a single file is not implemented because substantial string processing it would be required if thousands of files are selected. It would have been trivial if the selection was limited to a single directory (use a flag for each file and select the files with the flag set). However,
+.Nm
+allows selection across directories making it non-trivial to do that. Also, the buffer used to select is a compact one (no byte wasted) so \fBmemmove\fR() would be required to deselect each intermediate file. Considering these, we kept the solution simpler.
+.Sh FILE SIZE
+The minimum file size unit is byte (B). The rest are K, M, G, T, P, E, Z, Y (powers of 1024), same as the default units in \fIls\fR.
 .Sh ENVIRONMENT
 The SHELL, EDITOR (VISUAL, if defined) and PAGER environment variables take precedence
 when dealing with the !, e and p commands respectively. A single combination to arguments is supported for SHELL and PAGER.