Add project for workspaces tutorial

This is part of the work towards issue #437

doc/examples/developing/elements/base.bst

+kind: stack
+description: Base stack
+
+depends:
+- base/alpine.bst

doc/examples/developing/elements/base/alpine.bst

+kind: import
+description: |
+
+    Alpine Linux base runtime
+
+sources:
+- kind: tar
+
+  # This is a post doctored, trimmed down system image
+  # of the Alpine linux distribution.
+  #
+  url: alpine:integration-tests-base.v1.x86_64.tar.xz
+  ref: 3eb559250ba82b64a68d86d0636a6b127aa5f6d25d3601a79f79214dc9703639

doc/examples/developing/elements/hello.bst

+kind: manual
+description: |
+
+  Building manually
+
+# Depend on the base system
+depends:
+- base.bst
+
+# Stage the files/src directory for building
+sources:
+  - kind: local
+    path: files/src
+
+# Now configure the commands to run
+config:
+
+  build-commands:
+  - make PREFIX="%{prefix}"
+
+  install-commands:
+  - make -j1 PREFIX="%{prefix}" DESTDIR="%{install-root}" install

doc/examples/developing/files/src/Makefile

+# Sample makefile for hello.c
+#
+.PHONY: all install
+
+all: hello
+
+install:
+	install -d ${DESTDIR}${PREFIX}/bin
+	install -m 755 hello ${DESTDIR}${PREFIX}/bin
+
+hello: hello.c
+	$(CC) -Wall -o $@ $<

doc/examples/developing/files/src/hello.c

+/*
+ * hello.c - Simple hello world program
+ */
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+  printf("Hello World\n");
+  return 0;
+}

doc/examples/developing/project.conf

+# Unique project name
+name: running-commands
+
+# Required BuildStream format version
+format-version: 9
+
+# Subdirectory where elements are stored
+element-path: elements
+
+# Define an alias for our alpine tarball
+aliases:
+  alpine: https://gnome7.codethink.co.uk/tarballs/

doc/examples/developing/update.patch

+-- hello.c	2018-06-25 14:48:32.077568920 +0100
++++ hello.c	2018-06-25 14:49:23.025553785 +0100
+@@ -5,6 +5,6 @@
+ 
+ int main(int argc, char *argv[])
+ {
+-  printf("Hello World\n");
++  printf("Hello World\nWe can use workspaces!\n");
+   return 0;
+ }