fspath: allow unicode numbers and letters in remote names

Previously it was limited to plain ASCII (0-9, A-Z, a-z).

Implemented by adding \p{L}\p{N} alongside the \w in the regex,
even though these overlap it means we can be sure it is 100%
backwards compatible.

Fixes #6618

docs/content/docs.md

@@ -338,10 +338,18 @@ Will get their own names
 ### Valid remote names
 
 Remote names are case sensitive, and must adhere to the following rules:
- - May only contain `0`-`9`, `A`-`Z`, `a`-`z`, `_`, `-`, `.` and space.
+ - May contain number, letter, `_`, `-`, `.` and space.
  - May not start with `-` or space.
  - May not end with space.
 
+Starting with rclone version 1.61, any Unicode numbers and letters are allowed,
+while in older versions it was limited to plain ASCII (0-9, A-Z, a-z). If you use
+the same rclone configuration from different shells, which may be configured with
+different character encoding, you must be cautious to use characters that are
+possible to write in all of them. This is mostly a problem on Windows, where
+the console traditionally uses a non-Unicode character set - defined
+by the so-called "code page".
+
 Quoting and the shell
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