update docs about simd usage

.travis.yml

@@ -11,14 +11,10 @@ env:
     -
     - CARGO_CFG_HTTPARSE_DISABLE_SIMD=1
     - CARGO_CFG_HTTPARSE_DISABLE_SIMD_COMPILETIME=1 RUSTFLAGS="-C target_feature=+sse4.2"
-    #- CARGO_CFG_HTTPARSE_DISABLE_SIMD_COMPILETIME=1 RUSTFLAGS="-C target_feature=+avx2"
-    #- CARGO_CFG_HTTPARSE_DISABLE_SIMD_COMPILETIME=1 RUSTFLAGS="-C target_feature=+sse4.2,+avx2"
     - RUSTFLAGS="-C target_feature=+sse4.2"
-    #- RUSTFLAGS="-C target_feature=+avx2"
-    #- RUSTFLAGS="-C target_feature=+sse4.2,+avx2"
 
 matrix:
-    #fast_finish: true
+    fast_finish: true
     include:
         - rust: 1.10.0 # minimum Rust version
           script: # don't run tests, since dev-dependencies don't build on 1.10

src/lib.rs

@@ -10,7 +10,15 @@
 //! parsing internals use an `Iterator` instead of direct indexing, while
 //! skipping bounds checks.
 //!
-//! The speed is faster than picohttpparser, when SIMD is not available.
+//! With Rust 1.27.0 or later, support for SIMD is enabled automatically.
+//! If building an executable to be run on multiple platforms, and thus
+//! not passing `target_feature` or `target_cpu` flags to the compiler,
+//! runtime detection can still detect SSE4.2 or AVX2 support to provide
+//! massive wins.
+//!
+//! If compiling for a specific target, remembering to include
+//! `-C target_cpu=native` allows the detection to become compile time checks,
+//! making it *even* faster.
 #[cfg(feature = "std")]
 extern crate std as core;