Added kind operator

pkg/yqlib/doc/operators/kind.md

@@ -0,0 +1,77 @@
+
+## Get kind
+Given a sample.yml file of:
+```yaml
+a: cat
+b: 5
+c: 3.2
+e: true
+f: []
+g: {}
+h: null
+```
+then
+```bash
+yq '.. | kind' sample.yml
+```
+will output
+```yaml
+map
+scalar
+scalar
+scalar
+scalar
+seq
+map
+scalar
+```
+
+## Get kind, ignores custom tags
+Unlike tag, kind is not affected by custom tags.
+
+Given a sample.yml file of:
+```yaml
+a: !!thing cat
+b: !!foo {}
+c: !!bar []
+```
+then
+```bash
+yq '.. | kind' sample.yml
+```
+will output
+```yaml
+map
+scalar
+map
+seq
+```
+
+## Add comments only to scalars
+An example of how you can use kind
+
+Given a sample.yml file of:
+```yaml
+a:
+  b: 5
+  c: 3.2
+e: true
+f: []
+g: {}
+h: null
+```
+then
+```bash
+yq '(.. | select(kind == "scalar")) line_comment = "this is a scalar"' sample.yml
+```
+will output
+```yaml
+a:
+  b: 5 # this is a scalar
+  c: 3.2 # this is a scalar
+e: true # this is a scalar
+f: []
+g: {}
+h: null # this is a scalar
+```
+