預設用 rails 指令產出來就會有 .gitignore 檔了，以下是個修改過的範例：
# Ignore bundler config.
Gemfile.lock
bin/
.bundle
vendor/bundle
# Ignore the default SQLite database.
db/*.sqlite3
db/*.sqlite3-journal
# Ignore all logfiles and tempfiles.
log
tmp
# Project
.rbenv-version
.rbx
.rvmrc
.ruby-version
# YARD
.yardoc
yardoc/
doc/
# Global/OSX.gitignore
.DS_Store
# Files that might appear on external disk
.Spotlight-V100
.Trashes
# Global/Windows.gitignore
# Windows image file caches
Thumbs.db
Desktop.ini