Add docs for feature flags (#333)

src/lib.rs

@@ -116,6 +116,12 @@
 //! $ inferno-diff-folded folded2 folded1 | inferno-flamegraph --negate > diff1.svg
 //! ```
 //!
+//! # Feature flags
+//! All features below are enabled by default
+//! - `cli`: Also builds the `inferno` command-line tools
+//! - `multithreaded`: Enables multithreaded stack-collapsing
+//! - `nameattr`: Allows for adding customizing and adding attributes to the svg of [`flamegraph`]. See the `--nameattr` option for the flamegraph cli
+//!
 //! # Development
 //!
 //! This crate was initially developed through [a series of live coding sessions]. If you want to