feat: simple sensor panels with file-based data source (#7)

* add simulation mode for easier development

* improved sensor file watcher, poc cpu & mem usage

Trigger file read by rename event

* feat: system information sensor tool

Gather various sensor values with the sysinfo crate:
https://github.com/GuillaumeGomez/sysinfo
Values can be written to a sensor source file with the `--out` cmd line
option for the `asterctl` tool.

* ci: build sysinfo tool and include in build artifact

* feat: support integerDigits, decimalDigits sensor value format options

* docs: update documentation

Closes #6

.idea/runConfigurations/Run_demo.xml

@@ -1,7 +1,7 @@
 <component name="ProjectRunConfigurationManager">
   <configuration default="false" name="Run demo" type="CargoCommandRunConfiguration" factoryName="Cargo Command">
     <option name="buildProfileId" value="dev" />
-    <option name="command" value="run --package AOOstar-rs --bin AOOstar-rs -- --demo -d /dev/cu.usbserial-AB0KOHLS -w -c Monitor3.json" />
+    <option name="command" value="run --package aoostar-rs --bin asterctl -- --demo -c monitor.json" />
     <option name="workingDirectory" value="file://$PROJECT_DIR$" />
     <envs />
     <option name="emulateTerminal" value="true" />