Add new_tex_uwletter script and update README

Add new_tex_uwletter script (moved from ~/bin) with bug fixes: set -e,
quoted variables, WORK_DIR instead of TMPDIR, existence check for
destination, and mktemp inside the conditional. Update README to fix
stale URLs, ShareLaTeX -> Overleaf, MacOSX -> macOS, typo in
Dasgupta's email, and add script usage section.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

new_tex_uwletter

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+# Helper script to export LaTeX templates for new UW letters
+# Copyright (c) 2009-2016 Benjamin Mako Hill <mako@atdot.cc>
+# Released under the GPLv3 or later.
+
+set -e
+
+SOURCEDIR="$HOME/tex/uw_tex_letterhead"
+CURDIR=$(pwd)
+
+if [ -n "$1" ]
+then
+    if [ -e "$1" ]; then
+        echo "error: '$1' already exists"
+        exit 1
+    fi
+
+    WORK_DIR=$(mktemp -d)
+    cd "$SOURCEDIR"
+    git archive --format=tar mako | tar x -C "$WORK_DIR"
+    cd "$CURDIR"
+    mv "$WORK_DIR" "$1"
+    cd "$1"
+    mv "washington_letterhead_letter-matrix-deptartment.tex" "$(basename "$1").tex"
+
+    # create a symlink farm for the fonts
+    rm -rf ./fonts/*
+
+    # first create the directories
+    for fontdir in "${SOURCEDIR}/fonts/"*; do
+        mkdir "./fonts/$(basename "${fontdir}")"
+        # then the files
+        for fontfile in "${fontdir}/"*; do
+            ln -s "${fontfile}" "./fonts/$(basename "${fontdir}")/$(basename "${fontfile}")"
+        done
+    done
+else
+    echo "specify a directory where the template should go"
+fi