Added components doc in client.md

doc/client.md

@@ -10,6 +10,12 @@ This function calls the /update route, which will initiate the SSE connexion, re
 
 The calling cascade is initiated with the `nextInitCommand()` function (`SeaWebClientMain.js`), called just after the `loadFirstBlocks()` function. Every response of each command will be treated in the switch statement of the `successHandler()` function (in `SeaWebClientCommunication.js`). Specifically, the content of each block is dynamically created in JS when the response of the different init commands are received.
 
+### Components
+
+A component is composed of a JS file and its CSS file. They are grouped in the folder `client/components`. A component is basically a class that inherits from `HTMLELement`, and implement the method connectedCallback, where the HTML of the component has to be defined. Then, it has to be added to the customElements via the line `customElements.define("<component-name>", <ComponentClass>)`. The component's name has to contain dash, otherwise an error is thrown.
+
+The export popup and the dates popup are considered as components just to separate their code from the rest.
+
 ### About updating graphics
 
 - When the server is pushing data, the newly received data is appened to the current curves (on livemode).