add docs for try-catch-else (#48414)

ref #46928

Co-authored-by: Ian Butterworth <i.r.butterworth@gmail.com>
(cherry picked from commit d775750)

doc/src/manual/control-flow.md

@@ -819,6 +819,44 @@ no error has occurred, but the ability to unwind the stack and pass a value to a
 is desirable. Julia provides the [`rethrow`](@ref), [`backtrace`](@ref), [`catch_backtrace`](@ref)
 and [`current_exceptions`](@ref) functions for more advanced error handling.
 
+### `else` Clauses
+
+!!! compat "Julia 1.8"
+    This functionality requires at least Julia 1.8.
+
+In some cases, one may not only want to appropriately handle the error case, but also want to run
+some code only if the `try` block succeeds. For this, an `else` clause can be specified after the
+`catch` block that is run whenever no error was thrown previously. The advantage over including
+this code in the `try` block instead is that any further errors don't get silently caught by the
+`catch` clause.
+
+```julia
+local x
+try
+    x = read("file", String)
+catch
+    # handle read errors
+else
+    # do something with x
+end
+```
+
+!!! note
+    The `try`, `catch`, `else`, and `finally` clauses each introduce their own scope blocks, so if
+    a variable is only defined in the `try` block, it can not be accessed by the `else` or `finally`
+    clause:
+    ```jldoctest
+    julia> try
+               foo = 1
+           catch
+           else
+               foo
+           end
+    ERROR: UndefVarError: `foo` not defined
+    ```
+    Use the [`local` keyword](@ref local-scope) outside the `try` block to make the variable
+    accessible from anywhere within the outer scope.
+
 ### `finally` Clauses
 
 In code that performs state changes or uses resources like files, there is typically clean-up

doc/src/manual/variables-and-scoping.md

@@ -117,7 +117,7 @@ x = 1
 
 Note that the interactive prompt (aka REPL) is in the global scope of the module `Main`.
 
-## Local Scope
+## [Local Scope](@id local-scope)
 
 A new local scope is introduced by most code blocks (see above [table](@ref
 man-scope-table) for a complete list). If such a block is syntactically nested