Add Disclaimer about Lightning WIP to Guide intro page (#479)

* Add minimal entry on the Lightning Network to the glossary

* Add Tip on Guide intro page about work in progress on Lightning.

Author: danielnordh

guide.md

@@ -43,6 +43,14 @@ Illustration sources
 
 We designed this guide to help anyone navigate those complexities—regardless of where they live or work. We can’t imagine every possible use case, but we can help you build for them.
 
+{% include tip/tip.html %}
+
+This guide is a work in progress. We are currently adding information about the [Lightning Network]({{ '/guide/glossary/#lightning-network' | relative_url }}) on all relevant pages. 
+
+You can track the progress on this [Github issue]({{ 'https://github.com/BitcoinDesign/Guide/issues/478' }}).
+
+{% include tip/close.html %}
+
 ---
 
 ### [Getting started]({{ '/guide/getting-started/introduction/' | relative_url }})

guide/glossary/index.md

@@ -178,6 +178,10 @@ When an address receives bitcoin from another address, this is called an input.
 
 Bitcoin wallets and addresses are have both [public](#public-key) and [private keys](#private-key) associated to them. The private key controls access to funds and the ability to sign (approve) transactions.
 
+### Lightning Network
+
+The [Lightning Network]({{ 'https://lightning.network' }}) extends Bitcoin with payment channels to increase transaction speed and lower costs. It is becoming widely adopted and accepted as the preferred way to scale Bitcoin. 
+
 ### Miniscript
 
 A language for writing certain types of Bitcoin Scripts in a structured way. Miniscript is easier to read by developers, and also allows for various build-tools to help ensure that scripts are safe, valid, and efficient.