Fixed/enhanced some entries in the manpage

htop.1.in

@@ -246,21 +246,22 @@ The time the process was started.
 The ID of the CPU the process last executed on.
 .TP
 .B M_SIZE (VIRT)
-Size in memory of the total program size.
+The size of the virtual memory of the process.
 .TP
 .B M_RESIDENT (RES)
-The resident set size, i.e. the size of the text and data sections, plus stack
-usage.
+The resident set size (text + data + stack) of the process (i.e. the size of the
+process's used physical memory).
 .TP
 .B M_SHARE (SHR)
 The size of the process's shared pages.
 .TP
 .B M_TRS (CODE)
-The size of the text segment of the process (i.e. the size of the process's
+The text resident set size of the process (i.e. the size of the process's
 executable instructions).
 .TP
 .B M_DRS (DATA)
-The size of the data segment plus stack usage of the process.
+The data resident set size (data + stack) of the process (i.e. the size of anything
+except the process's executable instructions).
 .TP
 .B M_LRS (LIB)
 The library size of the process.