`nimble install --link` as replacement for "old" (<=0.13.1) `nimble develop`
with https://github.com/nim-lang/nimble/pull/913 (currently merged and slated for release in 0.14) `nimble develop` changed considerably its behaviour. as discussed in the forum (see [this](https://forum.nim-lang.org/t/8404#54212), [this](https://forum.nim-lang.org/t/8404#54460) and [this](https://forum.nim-lang.org/t/8404#54524) comments of the same thread discussing Nim 1.6.0 RC1) a viable option to keep supporting the workflows that old `nimble develop` allowed is to replicate its functionality in a `nimble install --link` command.

as an example workflow that was supported by old `nimble develop` (and would keep being supported by this `nimble install --link` is the following):
* you have nim package `mylib`, you clone it and put it in develop mode
* in another folder you have a standalone nim file (`standalone.nim`) that reproduces a bug happening in `mylib`. this standalone file has no project around it nor a nimble file.
* you run `nim r standalone` and the bug reproduces.
* you modify `mylib` and try again `nim r standalone`, maybe your bug is fixed, maybe not and you can go back and forth in modifying `mylib` changing stuff and adding echo statements and always running only `nim r standalone` until you are satisfied with this change

how did old `nimble.develop` was able to support this workflow?

- it [created a special `nimble-link` file](https://github.com/nim-lang/nimble/blob/d13f3b8ce288b4dc8c34c219a4e050aaeaf43fc9/src/nimble.nim#L985) inside folder `~/.nimble/pkgs/mylib#head` that looked like this:
```
/path-to-my-repo/mylib/mylib.nimble
/path-to-my-repo/mylib/src
```
- [nim is aware of this specific `nimble-link` format](https://github.com/nim-lang/Nim/blob/5e6680406f39b2b0b90d8b137285e066cc358d43/compiler/nimblecmd.nim#L126) and is able to follow the link