docs: added doc regarding parsing the pom.xml

docs/advanced-usage.md

@@ -468,12 +468,20 @@ steps:
 
 ## Java-version file
 If the `java-version-file` input is specified, the action will try to extract the version from the file and install it.
-Action is able to recognize all variants of the version description according to [jenv](https://github.com/jenv/jenv). 
-Valid entry options:
-```
-major versions: 8, 11, 16, 17
-more specific versions: 1.8.0.2, 17.0, 11.0, 11.0.4, 8.0.232, 8.0.282+8
-early access (EA) versions: 15-ea, 15.0.0-ea, 15.0.0-ea.2, 15.0.0+2-ea
-versions with specified distribution: openjdk64-11.0.2
-```
-If the file contains multiple versions, only the first one will be recognized.
+
+It is able to parse the following files as `java-version-file`:
+
+- `.java-version`: Action is able to recognize all variants of the version description according to [jenv](https://github.com/jenv/jenv).
+  Valid entry options:
+  ```
+  major versions: 8, 11, 16, 17
+  more specific versions: 1.8.0.2, 17.0, 11.0, 11.0.4, 8.0.232, 8.0.282+8
+  early access (EA) versions: 15-ea, 15.0.0-ea, 15.0.0-ea.2, 15.0.0+2-ea
+  versions with specified distribution: openjdk64-11.0.2
+  ```
+  If the file contains multiple versions, only the first one will be recognized.
+- `pom.xml` 
+  - Spring Boot: `<java.version>` under project properties.
+  - Maven compiler plugin
+    - Setting the [source](https://maven.apache.org/plugins/maven-compiler-plugin/examples/set-compiler-source-and-target.html).
+    - Setting the [release](https://maven.apache.org/plugins/maven-compiler-plugin/examples/set-compiler-release.html).