docs/library/gc: Fix grammar and improve readability of gc.threshold().

docs/library/gc.rst

@@ -41,24 +41,24 @@ Functions
 
 .. function:: threshold([amount])
 
-   Set or query additional GC allocation threshold. Normally, GC is
-   triggered when new allocation cannot be satisfied, i.e. on out of
-   memory (OOM) condition. If this function is called, in addition to
-   OOM, GC will be triggered each time after *amount* of bytes has been
-   allocated (in total, since the previous time such amount of bytes
-   had been allocated). *amount* is usually specified as less than the
-   full heap size, with the intention to trigger GC earlier than the
-   heap will be exhausted, and in the hope that early GC will prevent
-   excessive memory fragmentation. This is a heuristic measure, effect
-   of which will vary from an application to application, as well as
-   the optimal value of *amount* parameter.
-
-   Calling the function without argument will return current value of
-   the threshold. Value of -1 means a disabled allocation threshold.
+   Set or query the additional GC allocation threshold. Normally, a collection
+   is triggered only when a new allocation cannot be satisfied, i.e. on an
+   out-of-memory (OOM) condition. If this function is called, in addition to
+   OOM, a collection will be triggered each time after *amount* bytes have been
+   allocated (in total, since the previous time such an amount of bytes
+   have been allocated). *amount* is usually specified as less than the
+   full heap size, with the intention to trigger a collection earlier than when the
+   heap becomes exhausted, and in the hope that an early collection will prevent
+   excessive memory fragmentation. This is a heuristic measure, the effect
+   of which will vary from application to application, as well as
+   the optimal value of the *amount* parameter.
+
+   Calling the function without argument will return the current value of
+   the threshold. A value of -1 means a disabled allocation threshold.
 
    .. admonition:: Difference to CPython
       :class: attention
 
-      This function is MicroPython extension. CPython has a similar
+      This function is a MicroPython extension. CPython has a similar
       function - ``set_threshold()``, but due to different GC
       implementations, its signature and semantics are different.