Add md-to-clip custom completions

Resolves #414

* Syntax source https://github.com/command-line-interface-pages/v2-tooling/tree/main/md-to-clip

Author: Kissaki

custom-completions/md-to-clip/md-to-clip-completions.nu

@@ -0,0 +1,22 @@
+# Converter from TlDr format to Command Line Interface Pages format.
+# https://github.com/command-line-interface-pages/v2-tooling/tree/main/md-to-clip
+export extern "md-to-clip" [
+    file: path@"nu-complete md-to-clip mdfiles" # Source tldr page to convert
+    --help (-h)     # Display help
+    --version (-v)  # Display version
+    --author (-a)   # Display author
+    --email (-e)    # Display author email
+    --no-file-save  # Whether to display conversion result in stdout instead of writing it to a file
+    --output-directory : path@"nu-complete md-to-clip dirs"  # Directory where conversion result will be written
+    --special-placeholder-config: path  # Config with special placeholders
+]
+# "old-style long switch" flags are not covered because Nushell does not currently support them https://github.com/nushell/nushell/issues/5959
+# `-nfs`, `-od`, `-spc`
+
+def "nu-complete md-to-clip dirs" [] {
+  ls | where type == 'dir' | get name
+}
+
+def "nu-complete md-to-clip mdfiles" [] {
+  ls | where type == 'dir' or name ends-with '.md' | get name
+}