Document build steps for rdiff pkg

[#146010223]

Signed-off-by: Natalie Arellano <narellano@pivotal.io>

Author: Charlie Vieth

rdiff/update.bash

@@ -1,20 +1,46 @@
 # This is only here as an example and has not been tested!
 #
-# The build files must have already been generated by cmake.
+# This *must* be run from the rdiff directory where this
+# file is located!
 
-LIBRSYNC_DIR=""
-LIBRSYNC_BUILD_DIR=""
+# Root directory of librsync
+LIBRSYNC_DIR="PATH_TO_LIBRSYNC_SRC_DIR"
+
+# Directory where generated Makefile and generate source code will
+# be saved.
+LIBRSYNC_BUILD_DIR="$LIBRSYNC_DIR/build"
 
 if [[ ! -d "$LIBRSYNC_DIR" ]]; then
 	echo "Invalid LIBRSYNC_DIR: $LIBRSYNC_DIR"
 fi
 
-if [[ ! -d "$LIBRSYNC_BUILD_DIR" ]]; then
-	echo "Invalid LIBRSYNC_BUILD_DIR: $LIBRSYNC_BUILD_DIR"
-fi
+# librsync install: (uncomment to run)
+#
+# # This is where the library would be saved if 'make' is ran on the
+# # resulting build files.  This is not actually used, but is good to
+# # set (in case someone decides to run 'make install') as it prevents
+# # overwriting the librsync library in /usr/local.
+# LIBRSYNC_INSTALL_DIR="$LIBRSYNC_DIR/install"
+#
+# mkdir "$LIBRSYNC_BUILD_DIR"
+# mkdir "$LIBRSYNC_INSTALL_DIR"
+#
+# pushd "$LIBRSYNC_BUILD_DIR"
+# 	cmake \
+# 	  -DCMAKE_INSTALL_PREFIX:PATH="$LIBRSYNC_INSTALL_DIR" \
+# 	  -DCMAKE_BUILD_TYPE:STRING="Release" \
+# 	  "$LIBRSYNC_DIR"
+# popd
+#
+# if [[ ! -d "$LIBRSYNC_BUILD_DIR" ]]; then
+# 	echo "Invalid LIBRSYNC_BUILD_DIR: $LIBRSYNC_BUILD_DIR"
+# fi
 
+# Remove any C source code artifacts from rdiff directory.
 rm -vf *.[ch]
 
+# We need glob expansion - so $LIBRSYNC_DIR better not contain
+# any spaces!!
 cp $LIBRSYNC_BUILD_DIR/src/*.[ch]
 cp $LIBRSYNC_DIR/src/*.[ch]
 rm -v rdiff.c