Rectify license claims for code copied from Pharo

The CRC and Checksum classes were copied from Pharo in 2017.
The extension methods are also heavily based or directly copied from Pharo
during the same year. So far the copying was only documented in a
commit message from 2017, but the LICENSE file incorrectly claimed that the
code originated in the Squot project. Only the adaptations to make the code
work in Squeak originated in the Squot project. Consequently any copyright
on the original code contributed to Pharo still applies. Since Pharo no longer
keeps the authorship information from when it still used Monticello, I cannot
attribute this code more specifically than to the Pharo project as a whole.

Pharo 6 was released in June 2017 after the code was copied, that's why
the sources indicated in the LICENSE file point to Pharo 6.0.0. Also, no older
versions are available in the Pharo GitHub repository, and Pharo did not copy
the full Monticello history to their Git repository.

LICENSE

@@ -1,10 +1,18 @@
 This repository contains multiple packages:
-- Squot, Squit, VersionControl, Pharo-compatibility come from here
+- Squot, Squit, VersionControl come from here
+- Pharo-compatibility was also initialized here, but consists mainly of code that was
+  copied and adapted from Pharo, in order to make FileSystem-Git run in Squeak.
 - FileSystem-Git and FileSystem (FS-*) are forks of packages originally hosted elsewhere.
 - Squot-CoAuthorsExtension was originally a separate project.
 
 The packages originating here are released under the MIT license as described below.
 
+The code copied from Pharo in 2017 is released under the MIT license according to
+https://github.com/pharo-project/pharo/blob/6.0.0/src/System-Support.package/SmalltalkImage.class/instance/licenseStringTemplate.st,
+https://pharo.org/features, https://pharo.org/contribute (all last accessed 2022-07-10).
+The adapations to Squeak included here are also released under the MIT license
+as described below.
+
 The original FileSystem-Git was released under the MIT license according to 
 http://smalltalkhub.com/#!/~FileSystemGitDev/FileSystem-Git/ (last accessed 2019-02-15) 
 and http://ss3.gemstone.com/ss/FileSystem-Git.html (last accessed 2019-02-15).
@@ -16,11 +24,11 @@ http://www.squeaksource.com/fs.html (last accessed 2019-02-15).
 The additions and changes provided here are also released under the MIT license 
 as described below.
 
-===============================================================
-Squot, Squit, VersionControl, Pharo-compatibility packages,
-Squot-CoAuthorsExtension,
+=====================================================================
+Squot, Squit, VersionControl, Squot-CoAuthorsExtension,
 changes and additions to FileSystem and FileSystem-Git packages
-===============================================================
+and Squeak adaptations to the code in the Pharo-compatibility package
+=====================================================================
 
 MIT License