docs: mention how to build VPP outside git

Type: docs

Change-Id: Iceee9ef489f7f68049882651bb338311295ca12d
Signed-off-by: Vratko Polak <vrpolak@cisco.com>
diff --git a/docs/spelling_wordlist.txt b/docs/spelling_wordlist.txt
index 6a06b3b..21baa62 100644
--- a/docs/spelling_wordlist.txt
+++ b/docs/spelling_wordlist.txt
@@ -1352,6 +1352,7 @@
 xxx
 XXX
 xyz
+xz
 yaml
 Yaml
 YYMM