Corrected inaccurate build instructions and vague points in install instructions

Signed-off-by: Jacky Song <dixinlily@hotmail.com>

BUILDING.md

@@ -122,19 +122,30 @@ cmake -GXCode -T buildsystem=1 -Duse_mad="off" -Duse_id3tag=off ../tenacity
   
     ```
     $ git clone https://github.com/tenacityteam/tenacity/
+    $ cd tenacity
     ```
 
 2. Configure Tenacity using CMake:
-   ```
+   ```bash
    $ mkdir build && cd build
-   $ cmake -G "Unix Makefiles" -Duse_ffmpeg=loaded ../tenacity
+   $ cmake -G "Unix Makefiles" -Duse_ffmpeg=loaded ..
    ```
    By default, Debug build will be configured. To change that, pass `-DCMAKE_BUILD_TYPE=Release` to CMake.
 
 3. Build Tenacity:
-   ```
+   ```bash
    $ make -j`nproc`
    ```
+   Note that this may slow your computer down quite a bit. To avoid this, you can use the alternate command:
+   ```bash
+   $ make -j$(($(nproc)-2))
+   ```
+   This will use 2 fewer CPU cores than the default, which is to use the absolute maximum number of cores. Feel free to change this to `make -j$(($(nproc)-3))` if you want to use (MAX-3) cores, or any other custom values.
+   Alternatively, you can manually specify the number of CPU cores to use:
+   ```bash
+   $ make -j2
+   # Uses only 2 cores
+   ```
 
 4. Testing the build:
    Adding a "Portable Settings" folder allows Tenacity to ignore the settings of any existing Tenacity installation.