Broken links in docs

[Robyer]

I was looking at the docs page https://tesseract-ocr.github.io/tessdoc/ and there is broken link:

• External Projects / AddOns navigates to https://tesseract-ocr.github.io/AddOns.md which doesn't exists -> it should be https://tesseract-ocr.github.io/tessdoc/AddOns.html (change to .html and missing tessdoc part)

Similar situation is on the AddOns page on first link:

• User Projects - 3rd Party navigates to https://tesseract-ocr.github.io/tessdoc/User-Projects-%E2%80%93-3rdParty.md but it should be https://tesseract-ocr.github.io/tessdoc/User-Projects-%E2%80%93-3rdParty.html (change to .html)

I haven't checked other pages, so it's possible there are similar issues with these *.md* instead of .html**

[Robyer]

I sent PR (two separate ones as I did it via Github website) to fix these two links.

[Shreeshrii]

Thanks!