update README.md for JDK 16+ issues

[agebhar1]

…
[ERROR] Internal error has occurred in rule [diktat-ruleset:function-length]. Please make an issue on this bug at https://github.com/saveourtool/diKTat/.
                       As a workaround you can disable these inspections in yml config: <[TOO_LONG_FUNCTION]>.
                       Root cause of the problem is in […] file.
java.lang.ExceptionInInitializerError
…
    at java.lang.reflect.Method.invoke (Method.java:568)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private transient java.lang.Object java.lang.Throwable.backtrace accessible: module java.base does not "opens java.lang" to unnamed module @6dd93a21
    at java.lang.reflect.AccessibleObject.checkCanSetAccessible (AccessibleObject.java:354)
    at java.lang.reflect.AccessibleObject.checkCanSetAccessible (AccessibleObject.java:297)
    at java.lang.reflect.Field.checkCanSetAccessible (Field.java:178)
    at java.lang.reflect.Field.setAccessible (Field.java:172)
    at org.jetbrains.kotlin.com.intellij.util.ReflectionUtil.findFieldInHierarchy (ReflectionUtil.java:154)
…

[codecov]

Codecov Report

Merging #1573 (05f6164) into master (d39973f) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1573   +/-   ##
=========================================
  Coverage     82.12%   82.12%           
  Complexity     2314     2314           
=========================================
  Files           112      112           
  Lines          7845     7845           
  Branches       2034     2034           
=========================================
  Hits           6443     6443           
  Misses          480      480           
  Partials        922      922           

Flag	Coverage Δ
unittests	82.12% <ø> (ø)

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[nulls]

@agebhar1, thanks for the fix

[agebhar1]

You are welcome!