document supported search operators (#245)

docs/api/README.md

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 # API Docs
 
-This website is built using [Docusaurus](https://docusaurus.io/), a modern static website generator.
+This website is built using [Docusaurus](https://docusaurus.io/), a modern static website generator.
+
+Run `npm run start` to start the development server.

docs/search_operators.md

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+# Supported search operators
+
+* `A B C` - Searches for pages containing *all* of the terms A, B, or C. The terms are allowed to appear in different fields (url, title, body, etc.).
+
+* `"A B C"` - Searches for pages containing the exact phrase "A B C" with the words in that specific order. The terms must appear in the same field.
+
+* `site:example.com` - Restricts search results to only pages from the specified site example.com. It can also match subdomains `site:sub.example.com` or page prefixes `site:sub.example.com/page` which will both match `sub.example.com/page`, `sub.example.com/page/subpage`, `extra.sub.example.com/page` etc.
+
+* `linkto:example.com` - Finds pages that contain links pointing to the specified domain example.com. Uses the same matching logic as `site:` queries.
+
+* `intitle:A B` - Searches for pages where term A must appear in the title, while B can appear anywhere on the page.
+
+* `inbody:A B` - Searches for pages where term A must appear in the main body text, while B can appear anywhere.
+
+* `inurl:A B` - Searches for pages where term A must appear in the URL, while B can appear anywhere on the page.
+
+* `exacturl:https://example.com` - Finds the page with exactly the specified URL. This is mostly used for debugging to see if a specific page is indexed.
+
+* `A -B` - Searches for pages containing term A but not term B.