Watchman exists to watch files and record when they change. It can also trigger
actions (such as rebuilding assets) when matching files change.
* Watchman can recursively watch one or more directory trees (we call them
* Watchman does not follow symlinks. It knows they exist, but they show up the
same as any other file in its reporting.
* Watchman waits for a root to settle down before it will start to trigger
notifications or command execution.
* Watchman is conservative, preferring to err on the side of caution; it
considers files to be freshly changed when you start to watch them or when it
* You can query a root for file changes since you last checked, or the current
state of the tree
* You can subscribe to file changes that occur in a root