chore: regenerate README (#324)

This PR was generated using Autosynth. 🌈


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

```
2020-11-16 22:56:43,164 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-billingbudgets/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-11-16 22:56:44,074 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/9e14884d-1b7c-4738-93d4-eaee9bdf08e3/targets

- [ ] To automatically regenerate this PR, check this box.

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-billingbudgets.git",
-        "sha": "9d6dc32320005ee76b14c11c505cd1aad93dce4e"
+        "sha": "c8fc88522f9606f032f93c3fbbbab5581599d8f7"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "7db8a6c5ffb12a6e4c2f799c18f00f7f3d60e279"
+        "sha": "d5fc0bcf9ea9789c5b0e3154a9e3b29e5cea6116"
       }
     }
   ]

README.md

@@ -20,7 +20,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>15.0.0</version>
+      <version>15.1.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -41,7 +41,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-billingbudgets</artifactId>
-  <version>0.5.1</version>
+  <version>0.5.2</version>
 </dependency>
 
 ```