add readme with benchmark summary

README.md

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+# go-hauk
+
+Go port of the [Hauk](https://github.com/bilde2910/Hauk) location sharing backend.
+
+## why
+
+The original PHP implementation works fine but has some overhead. This port provides:
+
+- 345x higher throughput (45k vs 133 req/s)
+- 36x smaller image (16MB vs 578MB)
+- 3x lower memory footprint (8MB vs 25MB idle)
+- single static binary, no runtime dependencies
+- redis only (no memcached)
+
+## usage
+
+```
+docker run -p 8080:8080 \
+  -e HAUK_AUTH_METHOD=password \
+  -e HAUK_PASSWORD_HASH='$2a$10$...' \
+  -e HAUK_REDIS_ADDR=redis:6379 \
+  ghcr.io/parkan/go-hauk
+```
+
+## config
+
+all config via environment variables:
+
+| var | default | description |
+|-----|---------|-------------|
+| HAUK_LISTEN_ADDR | :8080 | listen address |
+| HAUK_PUBLIC_URL | http://localhost:8080/ | public url for share links |
+| HAUK_REDIS_ADDR | localhost:6379 | redis address (host:port or redis:// url) |
+| HAUK_AUTH_METHOD | password | auth method (password, htpasswd, ldap) |
+| HAUK_PASSWORD_HASH | | bcrypt hash for password auth |
+
+see `config/config.go` for full list.
+
+## compatibility
+
+drop-in replacement for the php backend. works with the existing android app and web frontend.
+
+## license
+
+same as upstream (apache 2.0).