command-instead-of-module: improve documentation (#2356)

* command-instead-of-module: improve documentation

* chore: auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/ansiblelint/rules/command_instead_of_shell.md

@@ -0,0 +1,30 @@
+# command-instead-of-shell
+
+This rule identifies uses of `shell` modules instead of a `command` one when
+this is not really needed. Shell is considerably slower than command and should
+be avoided unless there is a special need for using shell features, like
+environment variable expansion or chaining multiple commands using pipes.
+
+## Problematic Code
+
+```yaml
+---
+- name: Problematic example
+  hosts: localhost
+  tasks:
+    - name: Echo a message
+      ansible.builtin.shell: echo hello # <-- command is better in this case
+      changed_when: false
+```
+
+## Correct Code
+
+```yaml
+---
+- name: Correct example
+  hosts: localhost
+  tasks:
+    - name: Echo a message
+      ansible.builtin.command: echo hello
+      changed_when: false
+```