rename master branch to main.

README.md

@@ -6,6 +6,17 @@ The Attendance module was previously developed by
     Dmitry Pupinin, Novosibirsk, Russia,
     Artem Andreev, Taganrog, Russia.
 
+Branches
+--------
+The git branches here support the following versions.
+
+| Moodle version     | Branch      |
+| ----------------- | ----------- |
+| Mooodle 3.5   | MOODLE_35_STABLE |
+| Mooodle 3.6   | MOODLE_36_STABLE |
+| Moodle 3.7 | MOODLE_37_STABLE |
+| Moodle 3.8 and higher | main |
+
 # PURPOSE
 The Attendance module allows teachers to maintain a record of attendance, replacing or supplementing a paper-based attendance register.
 It is primarily used in blended-learning environments where students are required to attend classes, lectures and tutorials and allows