site.conf.sample: document oe-git-proxy required tools for HOSTTOOLS

The script oe-git-proxy uses some tools that may not be included
on HOSTTOOLS, thus add the proper documentation.

(From meta-yocto rev: 737702c175691db679d513a05b1800a14da35c74)

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/site.conf.sample

@@ -24,7 +24,9 @@ SCONF_VERSION = "1"
 #or
 #ALL_PROXY ?= "https://proxy.example.com:8080"
 # If you wish to use certain hosts without the proxy, specify them in NO_PROXY.
-# See the script for details on syntax.
+# See the script for details on syntax. The script oe-git-proxy uses some tools
+# that may not be included on HOSTTOOLS, thus  add them manually through
+# HOSTTOOLS += "getent seq"
 
 # Uncomment this to use a shared download directory
 #DL_DIR = "/some/shared/download/directory/"