doc: Add tar requirement to changes.rst

tar is used to build the kernel with CONFIG_IKHEADERS.

GNU tar 1.28 or later is required.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Documentation/process/changes.rst

@@ -60,6 +60,7 @@ openssl & libcrypto    1.0.0            openssl version
 bc                     1.06.95          bc --version
 Sphinx\ [#f1]_         1.7              sphinx-build --version
 cpio                   any              cpio --version
+GNU tar                1.28             tar --version
 gtags (optional)       6.6.5            gtags --version
 ====================== ===============  ========================================
 
@@ -175,6 +176,12 @@ You will need openssl to build kernels 3.7 and higher if module signing is
 enabled.  You will also need openssl development packages to build kernels 4.3
 and higher.
 
+Tar
+---
+
+GNU tar is needed if you want to enable access to the kernel headers via sysfs
+(CONFIG_IKHEADERS).
+
 gtags / GNU GLOBAL (optional)
 -----------------------------