doc/debugging_with_gdb.html: add introductory disclaimer The instructions in this document are useful but not reliable. Explain the situation up top.
doc/debugging_with_gdb.html: add introductory disclaimer
The instructions in this document are useful but not reliable.
Explain the situation up top.

Fixes issue 7471.

LGTM=josharian, iant
R=golang-codereviews, josharian, iant
CC=golang-codereviews
https://codereview.appspot.com/96830045

wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang