update the auplugin_fgets man page

Author: stevegrubb

docs/auplugin_fgets.3

@@ -48,23 +48,32 @@ and sets how it will be released when
 is called. The
 .I how
 parameter should be one of
-.B MEM_SELF_MANAGED,
-.B MEM_MALLOC,
-.B MEM_MMAP,
-or
-.B MEM_MMAP_FILE.
+.RS
+.TP 9
+.B MEM_SELF_MANAGED
+Internal buffer owned by fgets
+.TP
+.B MEM_MALLOC
+User-supplied malloc buffer; fgets frees it
+.TP
+.B MEM_MMAP
+User-supplied mmap buffer; fgets munmaps it
+.TP
+.B MEM_MMAP_FILE
+Read-only mmap file data
+.RE
+.IP
 The default is
 .B MEM_SELF_MANAGED
-which means no action is taken on the memory block.
-When
+which means its lifecycle is automatically handled. When
 .B MEM_MMAP_FILE
 is used, the buffer is treated as a preloaded buffer (the entire file) and no reads will be performed on the descriptor provided to
 .BR auplugin_fgets_r .
 The reentrant form
 .B auplugin_setvbuf_r
 operates on an explicit state handle.
 .PP
-These functions maintain static state and are therefore not thread safe.
+These functions maintain static state and are therefore not thread safe. For thread-safety, use the re-entrant variants.
 .SH RETURN VALUE
 .B auplugin_fgets
 returns -1 on error, 0 when no data is available, or the number of characters copied otherwise.