Update build documentation with missing log dependency (#296)

Author: dpad85

BUILD.md

@@ -16,6 +16,26 @@ brew install libtool
 brew install gmp
 ```
 
+## Required dependency
+
+This project currently depends on a fork of the `kodein-logs` library. This lib must be built manually and deployed to the local maven repository before being able to build `lightning-kmp`. To do so:
+1. clone [the GitHub repo](https://github.com/dpad85/Kodein-Log)
+```
+ git clone [email protected]:dpad85/Kodein-Log.git
+ cd Kodein-Log
+```
+2. checkout the `0.10.1-utc` tag
+```
+git checkout 0.10.1-utc
+```
+4. build and deploy the library:
+```
+./gradlew build
+./gradlew publishToMavenLocal
+```
+
+Note: this dependency is a temporary workaround and will be removed as soon as possible.
+
 ## Build
 
 You should start by cloning the repository locally: