Add diff, patch, and diffstat.

Fixes #36.

README.md

@@ -196,10 +196,14 @@ Notes:
 
 - If you ever need to write a tab literal in a command line in Bash (e.g. for the -t argument to sort), press **ctrl-v** **[Tab]** or write `$'\t'` (the latter is better as you can copy/paste it).
 
+- The standard tools for patching source code are `diff` and `patch`. See also `diffstat` for summary statistics of a diff. Note `diff -r` works for entire directories. Use `diff -r tree1 tree2 | diffstat` for a summary of changes.
+
 - For binary files, use `hd` for simple hex dumps and `bvi` for binary editing.
 
 - Also for binary files, `strings` (plus `grep`, etc.) lets you find bits of text.
 
+- For binary diffs (delta compression), use `xdelta3`.
+
 - To convert text encodings, try `iconv`. Or `uconv` for more advanced use; it supports some advanced Unicode things. For example, this command lowercases and removes all accents (by expanding and dropping them):
 ```sh
       uconv -f utf-8 -t utf-8 -x '::Any-Lower; ::Any-NFD; [:Nonspacing Mark:] >; ::Any-NFC; ' < input.txt > output.txt