Fix nbt bugs that cannot handle tagNames contains commas

nbt/README.md

@@ -1,6 +1,63 @@
 # NBT [![Go Reference](https://pkg.go.dev/badge/github.com/Tnze/go-mc/nbt.svg)](https://pkg.go.dev/github.com/Tnze/go-mc/nbt)
 
-This package implement the [Named Binary Tag](https://wiki.vg/NBT) format of Minecraft.
+This package implements the [Named Binary Tag](https://wiki.vg/NBT) format of Minecraft.
 
-The API is very similar to the standard library `encoding/json`. If you (high probability) have used that, it is easy to
-use this.
+The API is very similar to the standard library `encoding/json`.
+(But fix some its problem)
+If you (high probability) have used that, it is easy to use this.
+
+## Supported Struct Tags
+
+- `nbt` - The primary tag name. See below.
+- `nbtkey` - The key name of the field (Used to support commas `,` in tag names)
+
+### The `nbt` tag
+
+In most cases, you only need this one to specify the name of the tag. 
+
+The format of `nbt` struct tag: `<nbt tag>[,opt]`.
+
+It's a comma-separated list of options.
+The first item is the name of the tag, and the rest are options.
+
+Like this:
+```go
+type MyStruct struct {
+    Name string `nbt:"name"`
+}
+```
+
+To tell the encoder not to encode a field, use `-`:
+```go
+type MyStruct struct {
+    Internal string `nbt:"-"`
+}
+```
+
+To tell the encoder to skip the field if it is zero value, use `omitempty`:
+```go
+type MyStruct struct {
+    Name string `nbt:"name,omitempty"`
+}
+```
+
+Fields typed `[]byte`, `[]int32` and `[]int64` will be encoded as `TagByteArray`, `TagIntArray` and `TagLongArray` respectively by default.
+You can override this behavior by specifying encode them as`TagList` by using `list`:
+```go
+type MyStruct struct {
+    Data []byte `nbt:"data,list"`
+}
+```
+
+### The `nbtkey`
+
+Common issue with JSON standard libraries: inability to specify keys containing commas for structures.
+(e.g `{"a,b" : "c"}`)
+
+So this is a workaround for that:
+
+```go
+type MyStruct struct {
+    AB string `nbt:",omitempty" nbtkey:"a,b"`
+}
+```