Adding Static Analysis tools

In the open source, using static analysis tools is a good way to help us maintain the quality of our source code. So this time I tried to add them to my ConvertTxtToHTML project. I created a CONTRIBUTING file to help other contributors fix formatting issues, spot suspicious coding constructs, and alert the common errors.

Step 1: I using the [contributing generator](https://generator.contributing.md/) to generate a general contributing md file, and add the basic install steps.

Step 2: Add a Source Code Formatter
Since my project using Java, I using google-java-format which is a program that reformats Java source code to comply with Google Java Style.

I can run it in my cmd java -jar google-java-format-1.18.1-all-deps.jar -r ./src/application/*, and it automatically format and overwrite my java file, here is what I got. There were many lines had been revised, most of them are caused by space.

Step 3: Add a Linter
At first, I wanted to add spotBugs which is popular used.

But I couldn't find how to run it in cmd in it's github README, so I read it official website, still can't find the detail install cmd. At last, I found it's doc and know I can add the textui to run the command line user interface.

After setting all of these, I can run and get the version, but I met the error "Resource not found: java/lang/Object.class". I found a same error reported before on github, but the resolution didn't work for me...
I have to search other java linter, I searched and many tools only support the IDE. at last, I tried to use pmd which has a fantastic live demo, I did according to the demo and figure it out.

At last, I got my pmd result by using ./pmd-bin-7.0.0-rc4/bin/pmd check -R quickstart.xml -d src/ConvertTxtMdToHtml.java -f text --cache pmd.cache --report-file jdk-report.txt and got the result:

I got many errors which I didn't know before. I corrected my errors:

• Position literals first in String comparison：
  False: if (args.length == 0 || args[0].equals("-h") || args[0].equals("--help")) {
// Code implementation
}
  True: if (args.length == 0 || "-h".equals(args[0]) || "--help".equals(args[0])) {
// Code implementation
}

• ControlStatementBraces: This statement should have braces
  False:if (fileName.endsWith(".md")) title = convertLinks(title);
  True:if (fileName.endsWith(".md")) {
title = convertLinks(title); // convert links in MD file
}


• UnnecessaryLocalBeforeReturn: Consider simply returning the val
  False:String newLine = line.replaceAll("---", "<hr>");
return newLine;
  True:return line.replaceAll("---", "<hr>");

Step 4: Editor/IDE Integration
In order to using formatter and linter while we are writing code, I integrate them with my vscode, so I created .vscode folder and add the Java formatting and linting according to the vscode doc

At last, I have a stronger ConvertTxtToHTML project now!