Update README.rst

some small additions for clarity. please check to ensure meaning is preserved.
src: Avoid to call costly evbuffer_add() repeatedly

The profiler and benchmarking showed that calling evbuffer_add()
repeatedly is very costly. To avoid this, we buffer up small writes
into one large chunk and call evbuffer_add() less times.
nghttpd: More SSL_CTX options and support EDCHE cipher
nghttpd: Emit protocol id error only when verbose output is enabled
h2load: Support parellel native threads execution with -t option
Update README.rst
Update src/.gitignore
h2load: Fix crash with multi threading
nghttpx: Use LibsslGlobalLock
nghttpd: Add multi threading support
Update README.rst
nghttpd: Add -e option to toggle gzipped error response
nghttpx: Make socketpair in internal use non-block
nghttpd: Only emit content-encoding: gzip when error-gzip is on
src: Add EvbufferBuffer class to simplify the code base
src: Use jemalloc if available
Add --with-spdylay configure option
Update README.rst
Use 4086 as max DATA payload size to make DATA frame fit into 4K buffer
Filter supported flags in received frame