Update README.md: Document build with git submodules

README.md

@@ -72,13 +72,19 @@ Building
 Dependencies:
   - cpp-httplib: https://github.com/yhirose/cpp-httplib
   - SqliteModernCpp: https://github.com/SqliteModernCpp
+  - qssb.h: https://gitea.quitesimple.org/crtxcr/qssb.h
   - libseccomp: https://github.com/seccomp/libseccomp
   - sqlite3: https://sqlite.org/index.html
     
-The first two are header-only libraries that are already included here.
+The first three are header-only libraries that are included as a git submodule. The others must
+be installed, e. g. by using your distributions standard method.
 
 If all dependencies are available, run:
-```make release```
+```
+  git submodule init
+  git submodule update
+  make release
+```
 
 Setup
 =====