Document library dependencies installation path

The user may wish to compile sketches bundled with the installed library. In the absense of documentation, it would be challenging to determine where the installed libraries were located.

Author: per1234

README.md

@@ -22,7 +22,7 @@ YAML-format list of platform dependencies to install.
 
 Default `""`. If no `platforms` input is provided, the board's dependency will be automatically determined from the `fqbn` input and the latest version of that platform will be installed via Board Manager.
 
-If a platform dependency from a non-Board Manager source of the same name as another Board Manager source platform dependency is defined, they will both be installed, with the non-Board Manager dependency overwriting the Board Manager platform installation. This permits testing against a non-release version of a platform while using Board Manager to install the platform's tools dependencies. 
+If a platform dependency from a non-Board Manager source of the same name as another Board Manager source platform dependency is defined, they will both be installed, with the non-Board Manager dependency overwriting the Board Manager platform installation. This permits testing against a non-release version of a platform while using Board Manager to install the platform's tools dependencies.
 Example:
 ```yaml
 platforms: |
@@ -68,14 +68,16 @@ YAML-format list of library dependencies to install.
 
 Default `"- source-path: ./"`. This causes the repository to be installed as a library. If there are no library dependencies and you want to override the default, set the `libraries` input to an empty list (`- libraries: '-'`).
 
+Libraries are installed under the Arduino user folder at `~/Arduino/libraries`.
+
 Note: the original space-separated list format is also supported. When this syntax is used, the repository under test will always be installed as a library.
 
 #### Sources:
 
 ##### Library Manager
 
 Keys:
-- `name` - name of the library.
+- `name` - name of the library, as defined in the `name` field of its [library.properties](https://arduino.github.io/arduino-cli/library-specification/#libraryproperties-file-format) metadata file. The library will be installed to a folder matching the name, but with any spaces replaced by `_`.
 - `version` - version of the library to install. Default is the latest version.
 
 ##### Local path