Document FXIOS-9187 - Update README

[stevenbertolucci]

📜 Tickets

[Jira ticket](https://mozilla-hub.atlassian.net/browse/FXIOS-9187)
[Github issue](#20348)

💡 Description

To allow new contributors/users to successfully build the code after forking the project. The current README.md tells new contributors/users to cd into a sub-directory where bootstrap.sh file does not exist. This new README.md removes the cd firefox-ios line.

📝 Checklist

You have to check all boxes before merging

• Filled in the above information (tickets numbers and description of your work)
• Updated the PR name to follow our PR naming guidelines
• Wrote unit tests and/or ensured the tests suite is passing
• When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
• If needed, I updated documentation / comments for complex code and public methods
• If needed, added a backport comment (example @Mergifyio backport release/v120)

[DanielDervishi]

Hey Steven! The changes related to this issue were addressed in #20399. In that pr, the step "Change directories to the project root" was modified to indicate that users should be operating within the firefox-ios root directory. Its also useful for new contributors to have an explicit step in changing directories to "firefox-ios"

[stevenbertolucci]

Hi Daniel! Thanks for taking care of the updated README.md file!

I am taking an Open Source Software class at Oregon State University and my class required me to create a pull request based off an issue. I had to create one anyway to get credit for the project. I recently did get credit for it and you (or I) can close this pull request.

Again, thanks for taking care of my issue swiftly and I got to admit that contributing to a major project for the first time was very cool! I look forward contributing to many open source projects!