Fix formatting of README.md for better rendering

[akukanov]

I have no commit rights; someone who has please commit. Thanks.

[ldionne]

Committed as r350539, thanks!

README.md

 # Parallel STL 
 
 Parallel STL is an implementation of the C++ standard library algorithms with support for execution policies,
 as specified in ISO/IEC 14882:2017 standard, commonly called C++17. The implementation also supports the unsequenced 
 execution policy specified in Parallelism TS version 2 and proposed for the next version of the C++ standard in the 
-C++ working group paper P1001R1.
+C++ working group paper [P1001](https://wg21.link/p1001).
 Parallel STL offers efficient support for both parallel and vectorized execution of algorithms. For sequential 
 execution, it relies on an available implementation of the C++ standard library.
 
 ## Prerequisites
+
 To use Parallel STL, you must have the following software installed:
 * C++ compiler with:
   * Support for C++11
   * Support for OpenMP* 4.0 SIMD constructs
-* Threading Building Blocks (TBB) which is available to download in the GitHub [repository](https://github.com/01org/tbb/)
+* Threading Building Blocks (TBB) which is available for download at https://github.com/01org/tbb/
+
+## Known issues and limitations
 
-## Known Issues or limitations
-    unseq and par_unseq policies only have effect with compilers that
-        support '#pragma omp simd' or '#pragma simd'.
-    Parallel and vector execution is only supported for the algorithms
-        if random access iterators are provided, while for other iterator
-        types the execution will remain serial.
-    The following algorithms do not allow efficient SIMD execution:
-       includes, inplace_merge, merge, nth_element, partial_sort,
-        partial_sort_copy, set_difference, set_intersection,
-        set_symmetric_difference, set_union, sort, stable_partition,
-        stable_sort, unique.
-    The initial value type for exclusive_scan, inclusive_scan,
-        transform_exclusive_scan, transform_inclusive_scan shall satisfy
-        the DefaultConstructible requirements. A default constructed-instance
-        of the initial value type shall be the identity element for binary_op.
-    For max_element, min_element, minmax_element, partial_sort,
-        partial_sort_copy, sort, stable_sort the dereferenced value type of
-        the provided iterators shall be DefaultConstructible.
-    For remove, remove_if, unique the dereferenced value type of the provided
-        iterators shall be MoveConstructible.
-    The following algorithms require additional O(n) memory space for parallel
-        execution: copy_if, inplace_merge, partial_sort, partial_sort_copy,
-        partition_copy, remove, remove_if, rotate, sort, stable_sort, unique,
-        unique_copy.
+* `unseq` and `par_unseq` policies only have effect with compilers that support `#pragma omp simd` or `#pragma simd`.
+* Parallel and vector execution is only supported for the algorithms if random access iterators are provided,
+  while for other iterator types the execution will remain serial.
+* The following algorithms do not allow efficient SIMD execution: `includes`, `inplace_merge`, `merge`, `nth_element`,
+  `partial_sort`, `partial_sort_copy`, `set_difference`, `set_intersection`, `set_symmetric_difference`, `set_union`,
+  `sort`, `stable_partition`, `stable_sort`, `unique`.
+* The initial value type for `exclusive_scan`, `inclusive_scan`, `transform_exclusive_scan`, `transform_inclusive_scan`
+  shall be DefaultConstructible. A default constructed-instance of the initial value type shall be the identity element
+  for the specified binary operation.
+* For `max_element`, `min_element`, `minmax_element`, `partial_sort`, `partial_sort_copy`, `sort`, `stable_sort`
+  the dereferenced value type of the provided iterators shall be DefaultConstructible.
+* For `remove`, `remove_if`, `unique` the dereferenced value type of the provided iterators shall be MoveConstructible.
+* The following algorithms require additional O(n) memory space for parallel execution: `copy_if`, `inplace_merge`,
+  `partial_sort`, `partial_sort_copy`, `partition_copy`, `remove`, `remove_if`, `rotate`, `sort`, `stable_sort`,
+  `unique`, `unique_copy`.