Document slash command and query filter in docs for chat and search

docs/advanced.md

@@ -58,3 +58,24 @@ Note: *Only search can currently run in fully offline mode, not chat.*
 - Without Internet
   1. Copy each of the search models into their respective folders, `asymmetric`, `symmetric` and `image` under the `~/.khoj/search/` directory on the air-gapped machine
   2. Copy the khoj virtual environment directory onto the air-gapped machine, activate the environment and start and khoj as normal. E.g `source .venv/bin/activate && khoj`
+
+### Query Filters
+
+Use structured query syntax to filter entries from your knowledge based used by search results or chat responses.
+
+- **Word Filter**: Get entries that include/exclude a specified term
+  - Entries that contain term_to_include: `+"term_to_include"`
+  - Entries that contain term_to_exclude: `-"term_to_exclude"`
+- **Date Filter**: Get entries containing dates in YYYY-MM-DD format from specified date (range)
+  - Entries from April 1st 1984: `dt:"1984-04-01"`
+  - Entries after March 31st 1984: `dt>="1984-04-01"`
+  - Entries before April 2nd 1984 : `dt<="1984-04-01"`
+- **File Filter**: Get entries from a specified file
+  - Entries from incoming.org file: `file:"incoming.org"`
+- Combined Example
+  - `what is the meaning of life? file:"1984.org" dt>="1984-01-01" dt<="1985-01-01" -"big" -"brother"`
+  - Adds all filters to the natural language query. It should return entries
+    - from the file *1984.org*
+    - containing dates from the year *1984*
+    - excluding words *"big"* and *"brother"*
+    - that best match the natural language query *"what is the meaning of life?"*