[PATCH] ref-manual: add note explaining OE will identify missing packages

Add a note explaining that, if any required host tools are not
installed on the build host, doing a build will let the developer know
what they still need to install.

Signed-off-by: Robert P. J. Day <[email protected]>

---

diff --git a/documentation/ref-manual/system-requirements.rst b/documentation/ref-manual/system-requirements.rst
index 5171ca6ba..829b88293 100644
--- a/documentation/ref-manual/system-requirements.rst
+++ b/documentation/ref-manual/system-requirements.rst
@@ -160,6 +160,17 @@ large when covering all build scenarios using the Yocto Project. This
 section describes required packages according to Linux distribution and
 function.

+.. note::
+
+   If you don't have all of the required build packages as described below,
+   trying to build will almost certainly generate an error message similar to::
+
+      ERROR: The following required tools (as specified by HOSTTOOLS) appear
+      to be unavailable in PATH, please install them in order to proceed:
+        gawk
+
+   to let you know what's missing.
+
 .. _ubuntu-packages:

 Ubuntu and Debian