refactor documentation

docs/config-dynvars.md

@@ -0,0 +1,25 @@
+# Dynvariables entry
+
+The **dynvariables** entry (optional) contains an interpreted variables mapping.
+
+```yaml
+dynvariables:
+  <variable-name>: <shell-oneliner>
+```
+
+Dynvariables (*dynamic* variables) will be interpreted by the shell before being substituted.
+
+For example:
+```yaml
+dynvariables:
+  dvar1: head -1 /proc/meminfo
+  dvar2: "echo 'this is some test' | rev | tr ' ' ','"
+  dvar3: /tmp/my_shell_script.sh
+  user: "echo $USER"
+  config_file: test -f "{{@@ user_config @@}}" && echo "{{@@ user_config @@}}" || echo "{{@@ dfl_config @@}}"
+variables:
+  user_config: "profile_{{@@ user @@}}_uid.yaml"
+  dfl_config: "profile_default.yaml"
+```
+
+They have the same properties as [Variables](config-file.md#variables).