Building: Added mention of USE_SYSTEM_SRTP and USE_SYSTEM_JUICE

BUILDING.md

@@ -10,7 +10,9 @@ $ git submodule update --init --recursive
 
 ## Build with CMake
 
-The CMake library targets `libdatachannel` and `libdatachannel-static` respectively correspond to the shared and static libraries. The default target will build tests and examples. The option `USE_GNUTLS` allows to switch between OpenSSL (default) and GnuTLS, and the option `USE_NICE` allows to switch between libjuice as submodule (default) and libnice.
+The CMake library targets `libdatachannel` and `libdatachannel-static` respectively correspond to the shared and static libraries. The default target will build tests and examples.
+
+The option `USE_GNUTLS` allows to switch between OpenSSL (default) and GnuTLS, and the option `USE_NICE` allows to switch between libjuice as submodule (default) and libnice. The options `USE_SYSTEM_SRTP` and `USE_SYSTEM_JUICE` allow to link against the system library rather than building the submodule, for libsrtp and libjuice respectively.
 
 If you only need Data Channels, the option `NO_MEDIA` allows to make the library lighter by removing media support. Similarly, `NO_WEBSOCKET` removes WebSocket support.
 
@@ -28,19 +30,16 @@ $ make -j2
 $ cmake -B "$BUILD_DIR" -DUSE_GNUTLS=0 -DUSE_NICE=0 -G Xcode
 ```
 
-Xcode project is generated in *build/* directory.
+The XCode project is generated in `build` directory.
 
-#### Solving **Could NOT find OpenSSL** error
+#### Solving "Could NOT find OpenSSL" error
 
 You need to add OpenSSL root directory if your build fails with the following message:
-
 ```
-Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
-system variable OPENSSL_ROOT_DIR (missing: OPENSSL_CRYPTO_LIBRARY
-OPENSSL_INCLUDE_DIR)
+Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the system variable OPENSSL_ROOT_DIR (missing: OPENSSL_CRYPTO_LIBRARY OPENSSL_INCLUDE_DIR)
 ```
 
-for example:
+For example:
 ```bash
 $ cmake -B build -DUSE_GNUTLS=0 -DUSE_NICE=0 -G Xcode -DOPENSSL_ROOT_DIR=/usr/local/Cellar/openssl\@1.1/1.1.1h/
 ```