doc: replace 'IPC' -> 'RPC' in README.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
doc: fix spelling mistakes.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
doc: replace references from 'IPC' to 'RPC'.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>