Fixed broken links in 3 about.md files (#1238)

concepts/arrays/about.md

@@ -54,6 +54,7 @@ describe [| 5; 7; 9 |] // => "Other"
 [array-pattern]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching#array-pattern
 [array-module]: https://fsharp.github.io/fsharp-core-docs/reference/fsharp-collections-arraymodule.html
 [array-members]: https://docs.microsoft.com/en-us/dotnet/api/system.array?view=netcore-3.1
+[array-properties]: https://learn.microsoft.com/en-us/dotnet/api/system.array?view=netcore-3.1#methods
 
 You can also _discard_ a value when pattern matching; when you do _not_ care about a value in a specific case (i.e. you aren't going to _use_ a value) you can use an underscore (`'_'`) to signify this:
 

concepts/datetimes/about.md

@@ -15,3 +15,4 @@ When using a `DateTime` in a `sprintf` call, instead of manually converting the
 [properties]: https://docs.microsoft.com/en-us/dotnet/api/system.datetime?view=netcore-3.1#properties
 [to-string]: https://docs.microsoft.com/en-us/dotnet/api/system.datetime.tostring?view=netcore-3.1
 [object-placeholder]: https://fsharpforfunandprofit.com/posts/printf/#formatting-for-dummies
+[methods]: https://learn.microsoft.com/en-us/dotnet/api/system.datetime?view=netcore-3.1#methods

concepts/pattern-matching/about.md

@@ -1,6 +1,6 @@
 # About
 
-An `if/elif/else` expression can be used to conditionally execute logic. F# also has another, more powerful way to conditionally execute logic: [pattern matching][pattern-matching]. With pattern matching, a value can be tested against one or more _patterns_. An example of such a pattern is the [_constant pattern_][constant-pattern], which matches a value against a constant (e.g. `1` or `"hello"`).
+An `if/elif/else` expression can be used to conditionally execute logic. F# also has another, more powerful way to conditionally execute logic: [pattern matching][pattern-matching]. With pattern matching, a value can be tested against one or more _patterns_. An example of such a pattern is the [_constant pattern_][constant-patterns], which matches a value against a constant (e.g. `1` or `"hello"`).
 
 In F#, pattern matching is done through the `match` keyword: