docs: describe how to install from source with pnpm (#471)

Author: jkowalleck

README.md

@@ -92,21 +92,21 @@ written in _TypeScript_ and compiled for the target.
 
 ## Installation
 
-This package and the build results are available for _npm_, _yarn_ and _pnpm_:
+This package and the build results are available for _npm_, _pnpm_ and _yarn_:
 
 ```shell
 npm i -S @cyclonedx/cyclonedx-library
-yarn add @cyclonedx/cyclonedx-library
 pnpm add @cyclonedx/cyclonedx-library
+yarn add @cyclonedx/cyclonedx-library
 ```
 
 You can install the package from source,
 which will build automatically on installation:
 
 ```shell
 npm i -S github:CycloneDX/cyclonedx-javascript-library
+pnpm add github:CycloneDX/cyclonedx-javascript-library
 # not supported with yarn
-# not supported with pnpm
 ```
 
 ## Usage