doc: fine-tune the documentation of the 'm' RSP packet

Revise a sentence to avoid misinterpretation.  Move @cindex entries
before the text they index.  Refer to trace frames regarding partial
reads.

Approved-By: Eli Zaretskii <eliz@gnu.org>

gdb/doc/gdb.texinfo

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 1fd7267..20742d2 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -43094,24 +43094,25 @@
 @item m @var{addr},@var{length}
 @cindex @samp{m} packet
 Read @var{length} addressable memory units starting at address @var{addr}
-(@pxref{addressable memory unit}).  Note that @var{addr} may not be aligned to
-any particular boundary.
+(@pxref{addressable memory unit}).  Note that @var{addr} does not have to
+be aligned to any particular boundary.
 
+@cindex alignment of remote memory accesses
+@cindex size of remote memory accesses
+@cindex memory, alignment and size of remote accesses
 The stub need not use any particular size or alignment when gathering
 data from memory for the response; even if @var{addr} is word-aligned
 and @var{length} is a multiple of the word size, the stub is free to
 use byte accesses, or not.  For this reason, this packet may not be
 suitable for accessing memory-mapped I/O devices.
-@cindex alignment of remote memory accesses
-@cindex size of remote memory accesses
-@cindex memory, alignment and size of remote accesses
 
 Reply:
 @table @samp
 @item @var{XX@dots{}}
 Memory contents; each byte is transmitted as a two-digit hexadecimal number.
 The reply may contain fewer addressable memory units than requested if the
-server was able to read only part of the region of memory.
+server was reading from a trace frame memory and was able to read only part
+of the region of memory.
 @end table
 
 Unlike most packets, this packet does not support