Environment variable documentation update (fsprojects#2840)

Co-authored-by: Andrii Chebukin <[email protected]>

docs/guide/core-commandlineparsing.md

@@ -38,6 +38,8 @@ match DocoptResult.tryGetArgument "-m" results with
 
 *Note the following links are permalinks to old commits. They are intended only as examples. You are encouraged to look at the current version too, because it's likely to have been updated.*
 
+See also: https://fake.build/guide/core-targets.html#Script-with-arguments
+
 A more sophisticated example can be found in the fake runner: [<ins>src/app/Fake.netcore/Program.fs#L204-L259</ins>](https://github.com/fsharp/FAKE/blob/64d871f5065412fe7b233025e454ccf3b89e46d7/src/app/Fake.netcore/Program.fs#L204-L259)
 
 Or the target module:

docs/guide/core-targets.md

@@ -89,6 +89,12 @@ Now we have the following options:
 
 ## Script with arguments
 
+If you don't call `Target.initEnvironment()` before you use the `Environment` module, 
+then FAKE will only use system and inline environment variables 
+(e.g. Windows: `set mything=123`) instead of parsing the command line `-e` params.
+
+If you want multiple environment arguments, you can do `-e a=1 -e b=2`.
+
 Example:
 
 ```fsharp