_content/doc/modules/pruning: add a placeholder redirecting to “Managing dependencies”
_content/doc/modules/pruning: add a placeholder redirecting to “Managing dependencies”

I plan to add a more in-depth troubleshooting guide at this URL.
For now, I just need to URL to work so that I can point to it in
the 'go' command in Go 1.17 (in CL 332573).

For golang/go#36460

Change-Id: I95f03f76519dfb196ed6c9c13003b2ad9becf6c9
Reviewed-on: https://go-review.googlesource.com/c/website/+/334389
Trust: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Steve Traut <af4cad49c6f706d4616eefecc2c596e86c262fed@google.com>
Reviewed-by: Jay Conrod <f3fadaedc813344da5ec13b41e26596889cc5baa@google.com>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website