Documentation: Add minimum pahole version

A report was made in acmel/dwarves#26 about
pahole not being listed in the process/changes.rst file as being needed
for building the kernel, address that.

Link: acmel/dwarves#26
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/YZPQ6+u2wTHRfR+W@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/YZfzQ0DvHD5o26Bt@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: acmel

Documentation/process/changes.rst

@@ -35,6 +35,7 @@ GNU make               3.81             make --version
 binutils               2.23             ld -v
 flex                   2.5.35           flex --version
 bison                  2.0              bison --version
+pahole                 1.16             pahole --version
 util-linux             2.10o            fdformat --version
 kmod                   13               depmod -V
 e2fsprogs              1.41.4           e2fsck -V
@@ -108,6 +109,16 @@ Bison
 Since Linux 4.16, the build system generates parsers
 during build.  This requires bison 2.0 or later.
 
+pahole:
+-------
+
+Since Linux 5.2, if CONFIG_DEBUG_INFO_BTF is selected, the build system
+generates BTF (BPF Type Format) from DWARF in vmlinux, a bit later from kernel
+modules as well.  This requires pahole v1.16 or later.
+
+It is found in the 'dwarves' or 'pahole' distro packages or from
+https://fedorapeople.org/~acme/dwarves/.
+
 Perl
 ----