[BUGFIX] Add FIRST_INSTALL to .gitignore

In order to avoid accidentally committing a FIRST_INSTALL
for developers starting to contribute to TYPO3 Core
and using Core git repository for its basis local development
setup, the FIRST_INSTALL file is ignored from git.

Resolves: #91119
Releases: master, 10.4, 9.5
Change-Id: Iad459240bbc8a68892f03adf547373bc608f6a90
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64239


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Josef Glatz <josefglatz@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Josef Glatz <josefglatz@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>

.gitignore

@@ -57,6 +57,7 @@ nbproject
 /typo3conf/*
 /fileadmin/*
 /uploads/*
+/FIRST_INSTALL
 #
 # root .htaccess file
 /.htaccess