Add compatibility note about Nu version (#1057)

This is my response for #1051 

The syntax of this note is inspired by Rust _Cargo.toml_ and Python
_pyproject.toml_.

custom-completions/ssh/ssh-completions.nu

@@ -1,3 +1,5 @@
+# nu-version: 0.102.0
+
 export extern "ssh" [
     destination?: string@"nu-complete ssh-host"
     -4            # Forces ssh to use IPv4 addresses only.
@@ -41,11 +43,12 @@ module ssh-completion-utils {
         # │ 4 │                              │
         # ╰───┴──────────────────────────────╯
         let host = $in
-        let name = $host | get 0 | str trim | split row -r '\s+' | get 1
+        let $first_line = try { $host | first | str trim } catch { null }
         # Don't accept blocks like "Host *"
-        if ('*' in $name) {
+        if ($first_line | is-empty) or '*' in $first_line {
             null
         } else {
+            let name = $first_line |  split row -r '\s+' | get 1
             # May not contain hostname
             match ($host | slice 1.. | find -ir '^\s*Hostname\s') {
                 [] => null,
@@ -68,7 +71,7 @@ module ssh-completion-utils {
             includes: $include_lines
         }
     }
-    
+
 }