message: readme: add section about new crate features
diff: @@ -201,9 +201,36 @@ recommended for general use.
  [Documentation `regex-syntax`.](https://docs.rs/regex-syntax)
  +### Crate features
  +
  +This crate comes with several features that permit tweaking the trade off
  +between binary size, compilation time and runtime performance. Users of this
  +crate can selectively disable Unicode tables, or choose from a variety of
  +optimizations performed by this crate to disable.
  +
  +When all of these features are disabled, runtime match performance may be much
  +worse, but if you're matching on short strings, or if high performance isn't
  +necessary, then such a configuration is perfectly serviceable. To disable
  +all such features, use the following `Cargo.toml` dependency configuration:
  +
  +```toml
  +[dependencies.regex]
  +version = "1.3"
  +default-features = false
  +# regex currently requires the standard library, you must re-enable it.
  +features = ["std"]
  +```
  +
  +This will reduce the dependency tree of `regex` down to a single crate
  +(`regex-syntax`).
  +
  +The full set of features one can disable are
  +[in the "Crate features" section of the documentation](https://docs.rs/regex/*/#crate-features).
  +
  +
  ### Minimum Rust version policy
  -This crate's minimum supported `rustc` version is `1.28.1`.
  +This crate's minimum supported `rustc` version is `1.28.0`.
  The current **tentative** policy is that the minimum Rust version required
  to use this crate can be increased in minor version updates. For example, if
  