Started to write documentation on KiCAD integration

docs/usage/eda_integration.md

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+---
+layout: default
+title: EDA / KiCad integration
+parent: Usage
+---
+
+# EDA / KiCad integration
+
+Part-DB can function as central database for [EDA](https://en.wikipedia.org/wiki/Electronic_design_automation) or ECAD software used to design electronic schematics and PCBs.
+You can connect your EDA software and can view your available parts, with the data saved from Part-DB directly in your EDA software.
+Part-DB allows to configure additional metadata for the EDA, to associate symbols and footprints for use inside the EDA software, so the part becomes
+directly usable inside the EDA software.
+This also allows to configure available and usable parts and their properties in a central place, which is especially useful in teams, where multiple persons design PCBs.
+
+**Currently only KiCad is supported!**
+
+## KiCad Setup
+
+{: .important }
+> Part-DB uses the HTTP library feature of KiCad, which is experimental and not part of the stable KiCad 7 releases. If you want to use this feature, you need to install a KiCad nightly build (7.99 version). This feature will most likely also be part of KiCad 8.
+
+Part-DB should be accessible from the PCs with KiCAD. The URL should be stable (so no dynamically changing IP).
+You require a user account in Part-DB, which has the permission to access Part-DB API and create API tokens. Every user can has its own account, or you setup a shared read-only account.
+
+To connect KiCad with Part-DB do following steps:
+
+1. Create an API token on the user settings page for the KiCAD application and copy/save it, when it is shown. Currently KiCAD can only read Part-DB database, so a token with read only scope is enough.
+2. Create a file `partd.kicad_httplib` (or similar, only the extension is important) with the following content:
+```
+{
+    "meta": {
+        "version": 1.0
+    },
+    "name": "Part-DB library",
+    "description": "This KiCAD library fetches information externally from ",
+    "source": {
+        "type": "REST_API",
+        "api_version": "v1",
+        "root_url": "http://kicad-instance.invalid/en/kicad-api",
+        "token": "THE_GENERATED_API_TOKEN"
+    }
+}    
+```
+3. Replace the `root_url` with the URL of your Part-DB instance plus `/en/kicad-api` replace the `token` field value with the token you have generated in step 1.
+4. Open KiCad and add this created file as library in the KiCad symbol table under (Preferences --> Manage Symbol Libraries)
+
+If you then place a new part, the library dialog opens and you should be able to see the categories and parts from Part-DB.
+
+### How to associate footprints and symbols with parts
+
+Part-DB dont save any concrete footprints or symbols for the part. Instead Part-DB just contains a reference string in the part metadata, which points to a symbol/footprint in KiCads local library.
+
+You can define this on a per-part basis using the KiCad symbol and KiCad footprint field in the EDA tab of the part editor. Or you can define it at a category (symbol) or footprint level, to assign this value to all parts with this category and footprint.
+
+For example to configure the values for an BC547 transistor you would put `Transistor_BJT:BC547` on the parts Kicad symbol to give it the right schematic symbol in EEschema and `Package_TO_SOT_THT:TO-92` to give it the right footprint in PcbNew.