Improve --local-bin-path documentation

Author: mpilgrem

doc/global_flags.md

@@ -107,10 +107,13 @@ corresponding non-project specific configuration
 
 ## `--local-bin-path` option
 
-Pass the option `--local-bin-path <directory>` to specify the directory in which
-Stack installs executables. For further information, see the documentation for
-the corresponding non-project specific configuration
-[option](yaml_configuration.md#local-bin-path).
+Pass the option `--local-bin-path <directory>` to set the target directory for
+[`stack build --copy-bins`](build_command.md#-no-copy-bins-flag) and
+`stack install`. An absolute or relative path can be specified. A relative path
+at the command line is always assumed to be relative to the current directory.
+
+For further information, see the documentation for the corresponding non-project
+specific configuration [option](yaml_configuration.md#local-bin-path).
 
 ## `--lock-file` option
 

doc/yaml_configuration.md

@@ -918,7 +918,14 @@ Default (on Windows): `%APPDATA%\local\bin`
 
 Command line equivalent (takes precedence): `--local-bin-path` option
 
-Target directory for `stack install` and `stack build --copy-bins`.
+Specifies the target directory for
+[`stack build --copy-bins`](build_command.md#-no-copy-bins-flag) and
+`stack install`. An absolute or relative path can be specified.
+
+If the project-level configuration is provided in the `global-project` directory
+in the Stack root, a relative path is assumed to be relative to the current
+directory. Otherwise, it is assumed to be relative to the directory of the
+project-level configuration file.
 
 ### local-programs-path