Docs: Add README

README.md

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+# Introduction
+
+An implementation of electric door lock controller. Currently based on Arduino.
+Supporting NFC card and iButton devices as authentication keys.
+Currently uses built-in key database as authentication source, but remote source is planned,
+as defined in interfaces.
+
+# Building
+
+Arduino v1.8.5 or later is required as a base platform.
+Required libraries:
+- MFRC522 v1.3.6 or later
+- OneWire v2.3.3 or later
+Previous verions may work, but are untested.
+
+
+# Further development
+It is planned to abstract Arduino out, and move to
+more capable platform, not depending on Arduino.
+Also, LDAP support is planned instead of hardcoded key database,
+over TLS-secured connection, possibly with client certificate.