Added XML decoder (#1044)

pkg/yqlib/doc/operators/select.md

@@ -0,0 +1,41 @@
+# Select
+
+Select is used to filter arrays and maps by a boolean expression.
+
+## Select elements from array
+Given a sample.yml file of:
+```yaml
+- cat
+- goat
+- dog
+```
+then
+```bash
+yq eval '.[] | select(. == "*at")' sample.yml
+```
+will output
+```yaml
+cat
+goat
+```
+
+## Select and update matching values in map
+Given a sample.yml file of:
+```yaml
+a:
+  things: cat
+  bob: goat
+  horse: dog
+```
+then
+```bash
+yq eval '(.a.[] | select(. == "*at")) |= "rabbit"' sample.yml
+```
+will output
+```yaml
+a:
+  things: rabbit
+  bob: rabbit
+  horse: dog
+```
+