chore: regenerate README (googleapis#653)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2021-08-16 22:19:06,059 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-storage-nio/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-16 22:19:07,290 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/ad371dd6-3859-475d-867a-76b0fd4e5856/targets

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.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-storage-nio.git",
-        "sha": "de49ecb4819c6a9c22b4c685ae37e8f6fd67e7be"
+        "sha": "abf828fb57dc2b6721be647e696db65f53f556d2"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "ff01716e16d2c6e87eaf87197b753ac9fcbbed5d"
+        "sha": "a01e1a0bf70754f51450958b966bd673945d1e6e"
       }
     }
   ]

README.md

@@ -53,20 +53,20 @@ If you are using Maven without BOM, add this to your dependencies:
 If you are using Gradle 5.x or later, add this to your dependencies
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:20.9.0')
+implementation platform('com.google.cloud:libraries-bom:21.0.0')
 
 compile 'com.google.cloud:google-cloud-nio'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 
 ```Groovy
-compile 'com.google.cloud:google-cloud-nio:0.123.5'
+compile 'com.google.cloud:google-cloud-nio:0.123.6'
 ```
 
 If you are using SBT, add this to your dependencies
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-nio" % "0.123.5"
+libraryDependencies += "com.google.cloud" % "google-cloud-nio" % "0.123.6"
 ```
 
 ## Authentication