adding iqtree2 version 2.3.6

There's a new version of iqtree2!

And this time I remembered to include the Dockerfile in the PR!!! (Sorry about https://github.com/StaPH-B/docker-builds/pull/1015).

According to the release notes there are some new features and bug fixes.

All I did was copy the file for 2.3.4 and update the version arg.

The full diff

$ diff iqtree2/2.3.4/Dockerfile iqtree2/2.3.6/Dockerfile 
1c1
< ARG IQTREE2_VER="2.3.4"
---
> ARG IQTREE2_VER="2.3.6"

Pull Request (PR) checklist:

[X] Include a description of what is in this pull request in this message.
[X] The dockerfile successfully builds to a test target for the user creating the PR. (i.e. docker build --tag samtools:1.15test --target test docker-builds/samtools/1.15 )
[X] Directory structure as name of the tool in lower case with special characters removed with a subdirectory of the version number (i.e. spades/3.12.0/Dockerfile)
- [X] (optional) All test files are located in same directory as the Dockerfile (i.e. shigatyper/2.0.1/test.sh)
[X] Create a simple container-specific README.md in the same directory as the Dockerfile (i.e. spades/3.12.0/README.md)
- [X] If this README is longer than 30 lines, there is an explanation as to why more detail was needed
[X] Dockerfile includes the recommended LABELS
[X] Main README.md has been updated to include the tool and/or version of the dockerfile(s) in this PR
[X] Program_Licenses.md contains the tool(s) used in this PR and has been updated for any missing

StaPH-B / docker-builds