Add notes for translators.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>

doc/README.md

@@ -8,6 +8,12 @@ source code.
 the Markdown docs (reference manual, tutorials, etc.) distributed with
 this git repository.
 
+[po4a](http://po4a.alioth.debian.org/) is required for generating translated
+docs from the master (English) docs.
+
+[GNU gettext](http://www.gnu.org/software/gettext/) is required for managing
+the translation data.
+
 # Building
 
 To generate all the docs, just run `make docs` from the root of the repository.
@@ -38,3 +44,40 @@ http://johnmacfarlane.net/pandoc/README.html#pandocs-markdown
 
 A nice quick reference (for non-pandoc markdown) is at:
 http://kramdown.rubyforge.org/quickref.html
+
+# Notes for translators
+
+To start the translation for a new language, see po4a.conf at first.
+
+To generate .pot and .po files, do something like:
+
+~~~~
+po4a --copyright-holders="The Rust Project Developers" \
+    --package-name="Rust" \
+    --package-version="0.10-pre" \
+    -M UTF-8 -L UTF-8 \
+    po4a.conf
+~~~~
+
+(the version number must be changed if it is not 0.10-pre now.)
+
+Now you can translate documents with .po files, commonly used with gettext. If
+you are not familiar with gettext-based translation, please read the online
+manual linked from http://www.gnu.org/software/gettext/ . We use UTF-8 as the
+file encoding of .po files.
+
+When you want to make a commit, do the command below before staging your
+change:
+
+~~~~
+for f in doc/po/**/*.po; do
+    msgattrib --untranslated $f -o $f.strip
+    if [ -e $f.strip ]; then
+       mv $f.strip $f
+    else
+       rm $f
+    fi
+done
+~~~~ 
+
+This removes untranslated entries from .po files to save disk space.