add some small adjustments about the grammar of the literature in the README.md.

PR https://github.com/hnes/libaco/pull/17 by johnl <johnlunney@users.noreply.github.com> @johnlunney
Reviewed by Sen Han <00hnes@gmail.com>

README.md

@@ -12,9 +12,9 @@ Here is a brief summary of this project:
 
 - Along with the implementation of a production-ready C coroutine library, here is a detailed documentation about how to implement a *fastest* and *correct* coroutine library and also with a strict [mathematical proof](#proof-of-correctness);
 - It has no more than 700 LOC but has the full functionality which you may want from a coroutine library;
-- The [benchmark](#benchmark) part shows that one time of the context switching between coroutines only takes about *10 ns* (in the case of standalone stack) on the AWS c5d.large machine;
+- The [benchmark](#benchmark) part shows that a context switch between coroutines only takes about *10 ns* (in the case of standalone stack) on the AWS c5d.large machine;
-- User could choose to create a new coroutine with a *standalone stack* or with a *share stack* (could be shared with others);
+- User could choose to create a new coroutine with a *standalone stack* or with a *shared stack* (could be shared with others);
-- It is extremely memory efficient: *10,000,000* amount of co simultaneously to run only cost *2.8 GB* physical memory (run with tcmalloc, each co has a *120B* copy-stack size configuration).
+- It is extremely memory efficient: *10,000,000* coroutines simultaneously to run cost only *2.8 GB* physical memory (run with tcmalloc, each coroutine has a *120B* copy-stack size configuration).
 
 The phrase "*fastest*" in above means the fastest context switching implementation which complies to the Sys V ABI of Intel386 or AMD64.