docs: add go client readme

clients/ember-go/README.md

@@ -0,0 +1,157 @@
+# ember-go
+
+go gRPC client for the [ember](https://github.com/kacy/ember) cache server.
+
+## installation
+
+```bash
+go get github.com/kacy/ember-go
+```
+
+## quickstart
+
+```go
+package main
+
+import (
+    "context"
+    "fmt"
+    "log"
+
+    ember "github.com/kacy/ember-go"
+)
+
+func main() {
+    client, err := ember.Dial("localhost:6380")
+    if err != nil {
+        log.Fatal(err)
+    }
+    defer client.Close()
+
+    ctx := context.Background()
+
+    client.Set(ctx, "greeting", []byte("hello world"))
+    value, _ := client.Get(ctx, "greeting")
+    fmt.Println(string(value)) // hello world
+}
+```
+
+## authentication
+
+use `WithPassword` to authenticate on every request:
+
+```go
+client, err := ember.Dial("localhost:6380", ember.WithPassword("secret"))
+```
+
+the password is sent as gRPC metadata (`authorization` header) with each RPC call.
+
+## API reference
+
+### strings
+
+```go
+Get(ctx, key) ([]byte, error)
+Set(ctx, key, value, ...SetOption) (bool, error)
+Del(ctx, keys...) (int64, error)
+Exists(ctx, keys...) (int64, error)
+Incr(ctx, key) (int64, error)
+IncrBy(ctx, key, delta) (int64, error)
+Expire(ctx, key, seconds) (bool, error)
+TTL(ctx, key) (int64, error)
+```
+
+set options: `WithEX(seconds)`, `WithPX(millis)`, `WithNX()`, `WithXX()`
+
+### lists
+
+```go
+LPush(ctx, key, values...) (int64, error)
+RPush(ctx, key, values...) (int64, error)
+LPop(ctx, key) ([]byte, error)
+RPop(ctx, key) ([]byte, error)
+LRange(ctx, key, start, stop) ([][]byte, error)
+LLen(ctx, key) (int64, error)
+```
+
+### hashes
+
+```go
+HSet(ctx, key, fields) (int64, error)    // fields: map[string][]byte
+HGet(ctx, key, field) ([]byte, error)
+HGetAll(ctx, key) (map[string][]byte, error)
+HDel(ctx, key, fields...) (int64, error)
+```
+
+### sets
+
+```go
+SAdd(ctx, key, members...) (int64, error)
+SMembers(ctx, key) ([]string, error)
+SCard(ctx, key) (int64, error)
+```
+
+### sorted sets
+
+```go
+ZAdd(ctx, key, members...) (int64, error)  // members: ScoreMember{Member, Score}
+ZRange(ctx, key, start, stop, withScores) ([]ScoreMember, error)
+```
+
+### vectors
+
+```go
+VAdd(ctx, key, element, vector, ...VAddOption) (bool, error)
+VSim(ctx, key, query, count, ...VSimOption) ([]VSimResult, error)
+```
+
+vector options: `WithMetric(metric)`, `WithConnectivity(m)`, `WithEfConstruction(ef)`
+
+query options: `WithEfSearch(ef)`
+
+vectors are passed as `[]float32` — binary transport with no string parsing overhead.
+
+### server
+
+```go
+Ping(ctx) (string, error)
+FlushDB(ctx) error
+DBSize(ctx) (int64, error)
+```
+
+## context and error handling
+
+every method takes a `context.Context` as its first argument, following Go conventions. use contexts for timeouts and cancellation:
+
+```go
+ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+defer cancel()
+
+value, err := client.Get(ctx, "key")
+if err != nil {
+    // gRPC errors can be inspected with status.FromError(err)
+    log.Printf("get failed: %v", err)
+}
+```
+
+errors are standard gRPC status errors. use `google.golang.org/grpc/status` to inspect error codes.
+
+## connection details
+
+the gRPC server runs on port **6380** by default (separate from the RESP3 port 6379). the client uses an insecure connection by default.
+
+## development
+
+regenerate protobuf stubs after changing `proto/ember/v1/ember.proto`:
+
+```bash
+make proto-gen
+```
+
+requires `protoc`, `protoc-gen-go`, and `protoc-gen-go-grpc`.
+
+run tests:
+
+```bash
+make test
+```