Add instructions for releasing a fork

[sethfri]

While I was working on a patch for SwiftLint, I needed to be able to run it from the root of my project
in order to reproduce the bug. It took a lot of trial and error to figure out how to get my project to pick
up my fork's binaries. It'd be great to have these instructions as part of the repo to help future
contributors.

[codecov-commenter]

Codecov Report

Merging #3351 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3351   +/-   ##
=======================================
  Coverage   90.50%   90.51%           
=======================================
  Files         417      417           
  Lines       20432    20432           
=======================================
+ Hits        18493    18494    +1     
+ Misses       1939     1938    -1     

Impacted Files	Coverage Δ
...tFramework/Rules/Lint/ValidIBInspectableRule.swift	100.00% <0.00%> (+1.35%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6d2e8cf...3f8d8ab. Read the comment docs.

[jpsim]

There are much simpler ways to test changes in SwiftLint without cutting releases.

Using Xcode

1. git clone https://github.com/realm/SwiftLint.git
2. cd SwiftLint
3. xed .
4. Select the "swiftlint" scheme
5. cmd-opt-r open the scheme options
6. Set the "Arguments Passed On Launch" you want in the "Arguments" tab
7. Set the "Working Directory" you want in the "Options" tab
8. Hit "Run"

Arguments	Options

Then you can use the full power of Xcode/LLDB/Instruments to develop and debug your changes to SwiftLint.

Using the command line

1. git clone https://github.com/realm/SwiftLint.git
2. cd SwiftLint
3. swift build [-c release]
4. Use the produced swiftlint binary from the command line, either by running swift run [-c release] [swiftlint] [arguments] or by invoking the binary directly at .build/[release|debug]/swiftlint
5. [Optional] Attach LLDB: lldb -- .build/[release|debug]/swiftlint [arguments]

---

I'll make a PR adding this information to CONTRIBUTING.md to make it easier for contributors to learn about these development practices.

Update: PR here: #3360

[sethfri]

@jpsim Amazing! Thank you. I didn't know the Working Directory option existed, so that's the part I was struggling with. This makes things so much easier 🙏🏻