doc: UML diagrams for the nodes

Closes #2

doc_resources/nodes/.gitignore

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+*.png
+*.svg

doc_resources/nodes/class_diagram.puml

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+@startuml
+
+skinparam linestyle ortho
+left to right direction
+
+class "Supervisor" as sup{}
+class "BLE_advertiser" as ble{
+    + advertise(data)
+}
+class "Sensor" as sens{
+    + init(...)
+    + get_value()
+}
+class "Window_status" as win{}
+class "Hygrometer" as hygro{}
+class "Thermometer" as thermo{}
+class "CO2_level" as co2{}
+
+sup o-d- ble
+sup o-u- sens
+sens <|-l- win
+sens <|-u- hygro
+sens <|-u- thermo
+sens <|-r- co2
+
+@enduml

doc_resources/nodes/sequence_diagram.puml

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+@startuml
+
+skinparam sequenceMessageAlign center
+
+participant "Supervisor" as sup
+collections "Sensors" as sens
+participant "BLE_advertiser" as ble
+
+sup -> sens : get_value()
+sens --> sup : value
+sup -> ble : advertise(data)
+ble --> sup
+alt CO2 level above 400 OR windows is open
+    sup -> sup : sleep 2 minutes
+else else
+    sup -> sup : sleep for [last sleep time + 2 minutes]
+    note right : max sleep time = 30 minutes
+end
+
+@enduml