add a smol README

filter_parser/README.md

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+# Filter parser
+
+This workspace is dedicated to the parsing of the MeiliSearch filters.
+
+Most of the code and explanation are in the [src/lib.rs]. Especially, the BNF of the filters at the top of this file.
+
+The parser use [nom](https://docs.rs/nom/) to do most of its work and [nom-locate](https://docs.rs/nom_locate/) to keep track of what we were doing when we encountered an error.
+
+## Cli
+A simple main is provided to quick-test if a filter can be parsed or not without bringing milli.
+It takes one argument and try to parse it.
+```
+cargo run -- 'field = value' # success
+cargo run -- 'field = "doggo' # error => missing closing delimiter "
+```
+
+## Fuzz
+The workspace have been fuzzed with [cargo-fuzz](https://rust-fuzz.github.io/book/cargo-fuzz.html).
+
+### Setup
+You'll need rust-nightly to execute the fuzzer.
+
+```
+cargo install cargo-fuzz
+```
+
+### Run
+```
+cargo fuzz run parse
+```
+
+## What to do if you find a bug in the parser
+
+- Write a test at the end of the [src/lib.rs] to ensure it never happens again.
+- Add a file in [fuzz/corpus/parse/] with your filter to help the fuzzer finding new bug.