add mkcd workflow (#150)

* add mkcd workflow

`mkdir {dirname} && cd $_`

* chore: add `shell` tag, set shells to bash/zsh

cuz `$_` might be not a thing in other shells like fish

---------

Co-authored-by: elvis kahoro <elvis@warp.dev>

Author: blinpete

specs/shell/make_a_dir_and_change_into.yaml

@@ -0,0 +1,15 @@
+---
+name: Make a directory and change into it
+command: mkdir {{dirname}} && cd $_
+tags:
+  - shell
+description: Runs `mkdir` followed by `cd`. Generated by Warp AI.
+arguments:
+  - name: dirname
+    description: The directory name to make and get into
+source_url: "https://www.craft.do/s/1BYQC2mvGK82DC"
+author: blinpete
+author_url: "https://github.com/blinpete"
+shells:
+  - Zsh
+  - Bash