docs: bump dependency examples to 0.6 (were 0.4) (#44)

README and docs/tutorial.md showed 0.4 in the Maven/Gradle dependency
snippets — two releases behind the current 0.6 on Maven Central. Users
copy-pasting got a stale version. No other API drift found: dict-id docs
match the 0.6 ZstdDictionaryId surface, refPrefix is documented in how-to,
and supported.md's symbol counts are still accurate.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

README.md

@@ -45,7 +45,7 @@ the build runs on any OS/arch.
 <dependency>
   <groupId>io.github.dfa1.zstd</groupId>
   <artifactId>zstd-platform</artifactId>
-  <version>0.4</version>
+  <version>0.6</version>
 </dependency>
 ```
 
@@ -58,7 +58,7 @@ plus only the `zstd-native-<classifier>` you target.
     <dependency>
       <groupId>io.github.dfa1.zstd</groupId>
       <artifactId>zstd-bom</artifactId>
-      <version>0.4</version>
+      <version>0.6</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>

docs/tutorial.md

@@ -14,12 +14,12 @@ runs on any OS/arch:
 <dependency>
   <groupId>io.github.dfa1.zstd</groupId>
   <artifactId>zstd-platform</artifactId>
-  <version>0.4</version>
+  <version>0.6</version>
 </dependency>
 ```
 
 ```groovy
-implementation("io.github.dfa1.zstd:zstd-platform:0.4")
+implementation("io.github.dfa1.zstd:zstd-platform:0.6")
 ```
 
 That pulls all six natives (~3.8 MB, five unused per platform). When you target a
@@ -32,7 +32,7 @@ the matching classifier:
     <dependency>
       <groupId>io.github.dfa1.zstd</groupId>
       <artifactId>zstd-bom</artifactId>
-      <version>0.4</version>
+      <version>0.6</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -53,7 +53,7 @@ the matching classifier:
 ```
 
 ```groovy
-implementation(platform("io.github.dfa1.zstd:zstd-bom:0.4"))
+implementation(platform("io.github.dfa1.zstd:zstd-bom:0.6"))
 implementation("io.github.dfa1.zstd:zstd")
 runtimeOnly("io.github.dfa1.zstd:zstd-native-osx-aarch64")
 ```