Added another new recipe

pkg/yqlib/doc/usage/recipes.md

@@ -160,10 +160,10 @@ Given a sample.yml file of:
 ```yaml
 var0: string0
 var1: string1
-ary0:
-  - aryval0
-  - aryval1
-  - aryval2
+fruit:
+  - apple
+  - banana
+  - peach
 ```
 then
 ```bash
@@ -176,12 +176,51 @@ will output
 ```yaml
 var0='string0'
 var1='string1'
-ary0=('aryval0','aryval1','aryval2')
+fruit=('apple','banana','peach')
 ```
 
 ### Explanation:
 - `.[]` matches all top level elements
-- We need a string expression for each of the different types that will product the bash syntax, we'll use the union operator , to join them together
+- We need a string expression for each of the different types that will produce the bash syntax, we'll use the union operator, to join them together
 - Scalars, we just need the key and quoted value: `( select(kind == "scalar") | key + "='" + . + "'")`
 - Sequences (or arrays) are trickier, we need to quote each value and `join` them with `,`: `map("'" + . + "'") | join(",")`
 
+## Custom format with nested data
+Like the previous example, but lets handle nested data structures. In this custom example, we're going to join the property paths with _. The important thing to keep in mind is that our expression is not recursive (despite the data structure being so). Instead we match _all_ elements on the tree and operate on them.
+
+Given a sample.yml file of:
+```yaml
+simple: string0
+simpleArray:
+  - apple
+  - banana
+  - peach
+deep:
+  property: value
+  array:
+    - cat
+```
+then
+```bash
+yq '.. |(
+	( select(kind == "scalar" and parent | kind != "seq") | (path | join("_")) + "='" + . + "'"),
+	( select(kind == "seq") | (path | join("_")) + "=(" + (map("'" + . + "'") | join(",")) + ")")
+)' sample.yml
+```
+will output
+```yaml
+simple='string0'
+deep_property='value'
+simpleArray=('apple','banana','peach')
+deep_array=('cat')
+```
+
+### Explanation:
+- You'll need to understand how the previous example works to understand this extension.
+- `..` matches _all_ elements, instead of `.[]` from the previous example that just matches top level elements.
+- Like before, we need a string expression for each of the different types that will produce the bash syntax, we'll use the union operator, to join them together
+- This time, however, our expression matches every node in the data structure.
+- We only want to print scalars that are not in arrays (because we handle the separately), so well add `and parent | kind != "seq"` to the select operator expression for scalars
+- We don't just want the key any more, we want the full path. So instead of `key` we have `path | join("_")`
+- The expression for sequences follows the same logic
+