cmd/tsidp: remove backticks in README in shell example

Fixes #15818

Change-Id: I7a6f4c7368fed74b865a63acdea4559c3d0a0d09
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f