Transform parallelism md to rst (#380)

Author: steff456

spec/design_topics/parallelism.md renamed to spec/design_topics/parallelism.rst

@@ -1,4 +1,5 @@
-# Parallelism
+Parallelism
+===========
 
 Parallelism is mostly, but not completely, an execution or runtime concern
 rather than an API concern. Execution semantics are out of scope for this API
@@ -7,7 +8,7 @@ involves how libraries allow users to exercise control over the parallelism
 they offer, such as:
 
 - Via environment variables. This is the method of choice for BLAS libraries and libraries using OpenMP.
-- Via a keyword to individual functions or methods. Examples include the `n_jobs` keyword used in scikit-learn and the `workers` keyword used in SciPy.
+- Via a keyword to individual functions or methods. Examples include the ``n_jobs`` keyword used in scikit-learn and the ``workers`` keyword used in SciPy.
 - Build-time settings to enable a parallel or distributed backend.
 - Via letting the user set chunk sizes. Dask uses this approach.
 
@@ -19,5 +20,5 @@ coordination of parallelization behavior in a stack of Python libraries are:
 2. A common library providing a parallelization layer
 
 Option (1) may possibly fit in a future version of this array API standard.
-[array-api issue 4](https://github.com/data-apis/array-api/issues/4) contains
+`array-api issue 4 <https://github.com/data-apis/array-api/issues/4>`_ contains
 more detailed discussion on the topic of parallelism.