[Buildroot] [RFC 1/1] docs/adding-packages-generic.txt: Add note if package does not use source

[Vadim Kochan]

Add some description how to allow to add package which does not need
any source code.

Signed-off-by: Vadim Kochan <vadim4j at gmail.com>
---
 docs/manual/adding-packages-generic.txt | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/docs/manual/adding-packages-generic.txt b/docs/manual/adding-packages-generic.txt
index 7be1754f54..96a57a519a 100644
--- a/docs/manual/adding-packages-generic.txt
+++ b/docs/manual/adding-packages-generic.txt
@@ -223,8 +223,13 @@ not and can not work as people would expect it should:
   which Buildroot will use to download the tarball from
   +LIBFOO_SITE+. If +HOST_LIBFOO_SOURCE+ is not specified, it defaults
   to +LIBFOO_SOURCE+. If none are specified, then the value is assumed
-  to be +libfoo-$(LIBFOO_VERSION).tar.gz+. +
-  Example: +LIBFOO_SOURCE = foobar-$(LIBFOO_VERSION).tar.bz2+
+  to be +libfoo-$(LIBFOO_VERSION).tar.gz+.
+  In case when the package does not use any source code (e.g. only performs
+  some target/host altering), then +LIBFOO_SOURCE+ should be specified
+  with empty value. +
+  Examples:
+    +LIBFOO_SOURCE = foobar-$(LIBFOO_VERSION).tar.bz2+
+    +LIBFOO_SOURCE =
 
 * +LIBFOO_PATCH+ may contain a space-separated list of patch file
   names, that Buildroot will download and apply to the package source
-- 
2.14.1