If you absolutely don't want to use 3rd party software(including open-source), then just simply paste in your wallet address or qr code. Or if you want to be slightly more fancy, add a donate button(on your menu bar or at the bottom of the page) and use a modal pop-up with your wallets address/qrcode when clicked.
This is absolutely great alternative to collect payments, tips, or donations from websites. Along with this, it requires some sort of javascript to make more fancy functions such as pop-ups and other accessible details of transactions. If the website is developed using WordPress, then there are so many plugins for it.
My own Suggestion: Currently BTC transactions are costly just because of higher transaction and network fees. So it's always better to accept low transaction fees altcoins as Tip. It will definitely save lots of money spent on fees for transactions and networks along with the time required for transaction completion.