Update to link to Calendar PR

Standard-Library-Coverage.md

@@ -16,7 +16,7 @@
 | [bisect](https://docs.python.org/3/library/bisect.html#module-bisect) |  Array bisection algorithms for binary searching. | ✅ | [micropython-lib](https://github.com/micropython/micropython-lib/tree/master/python-stdlib/bisect)
 | [builtins](https://docs.python.org/3/library/builtins.html#module-builtins) |  The module that provides the built-in namespace. | ✅ | [built-in](https://docs.micropython.org/en/latest/library/builtins.html) 
 | [bz2](https://docs.python.org/3/library/bz2.html#module-bz2) |  Interfaces for bzip2 compression and decompression. | ❌ | 
-| [calendar](https://docs.python.org/3/library/calendar.html#module-calendar) |  Functions for working with calendars, including some emulation of the Unix cal program. | ❌ | 
+| [calendar](https://docs.python.org/3/library/calendar.html#module-calendar) |  Functions for working with calendars, including some emulation of the Unix cal program. | ❌ | See [#521](https://github.com/micropython/micropython-lib/pull/521)
 | [cmath](https://docs.python.org/3/library/cmath.html#module-cmath) |  Mathematical functions for complex numbers. | ✅ | [built-in](https://docs.micropython.org/en/latest/library/cmath.html)
 | [cmd](https://docs.python.org/3/library/cmd.html#module-cmd) |  Build line-oriented command interpreters. | ✅ | [micropython-lib](https://github.com/micropython/micropython-lib/tree/master/python-stdlib/cmd)
 | [code](https://docs.python.org/3/library/code.html#module-code) |  Facilities to implement read-eval-print loops. | ❌ |