Deprecated the Obsidian watcher in favor of the AW plugin for Obsidian

[StoppingBuck]

The Obsidian watcher seems to be dead, with the latest commit being 2 years ago and several issues mentioning it is broken. By contrast, the ActivityWatch plugin for Obsidian works fine and does the exact same thing, just by having Obsidian push the information to AW instead of having AW watch for it.

This PR adds this information

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[!IMPORTANT] Deprecated aw-watcher-obsidian in favor of the ActivityWatch plugin for Obsidian in watchers.rst.

• Deprecation:
  • Deprecated aw-watcher-obsidian in watchers.rst.
  • Added recommendation to use the ActivityWatch community plugin for Obsidian.

^{This description was created by for b3312e2c998c52ce78358dc0aa92e36ea66e866d. It will automatically update as commits are pushed.}