docs: update for ipc/cli, tidy a bit

docs/Dynamic values.md

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+In some configuration locations, Ironbar supports dynamic values, 
+meaning you can inject content into the bar from an external source.
+
+Currently two dynamic content sources are supported - scripts and ironvars.
+
+## Dynamic String
+
+Dynamic strings can contain any mixture of static string elements, scripts and variables.
+
+Scripts should be placed inside `{{double braces}}`. Both polling and watching scripts are supported.
+
+Variables use the standard `#name` syntax. Variables cannot be placed inside scripts.
+
+To use a literal hash, use `##`. This is only necessary outside of scripts.
+
+Example:
+
+```toml
+label = "{{cat greeting.txt}}, #subject"
+```
+
+## Dynamic Boolean
+
+Dynamic booleans can use a single source of either a script or variable to control a true/false value.
+
+For scripts, you can just write these directly with no notation. 
+Only polling scripts are supported. 
+The script exit code is used, where `0` is `true` and any other code is `false.
+
+For variables, use the standard `#name` notation. 
+An empty string, `0` and `false` are treated as false. 
+Any other value is true.
+
+Example:
+
+```toml
+show_if = "exit 0" # script
+show_if = "#show_module" # variable
+```