Wrap especially important sections in mdbook "warning"

src/guide/receive_onchain.md

@@ -72,7 +72,12 @@ In order to receive funds you first have to be connected to an [LSP](connecting_
 </section>
 </custom-tabs>
 
-It's important to be aware that the swap information provided includes maximum and minimum limits. Users must be informed of these limits because if the amount transferred to the swap address falls outside this valid range, the funds will not be successfully received via lightning. In such cases, a refund will be necessary.
+<div class="warning">
+<h4>Developer note</h4>
+
+The `swap_info` above includes maximum and minimum limits. Your application's users must be informed of these limits because if the amount transferred to the swap address falls outside this valid range, the funds will not be successfully received via lightning. In such cases, a refund will be necessary.
+
+</div>
 
 ## Get the in-progress Swap
 

src/guide/send_onchain.md

@@ -71,10 +71,15 @@ First, fetch the current reverse swap fees:
 </section>
 </custom-tabs>
 
+<div class="warning">
+<h4>Developer note</h4>
+
 The reverse swap will involve two on-chain transactions, for which the mining fees can only be estimated. They will happen
 automatically once the process is started, but the last two values above are these estimates to help you get a picture
 of the total costs.
 
+</div>
+
 Fetching the fees also tells you what is the range of amounts the service allows:
 
 <custom-tabs category="lang">